BOSTON — Cleveland Cavaliers general manager Koby Altman proudly waited outside the visiting locker room after the final buzzer to give LeBron James and the players on his victorious new-look team an appreciative fist pound on Sunday afternoon. Injured forward Kevin Love yelled out, “There you go! There you go!” Sharpshooter Kyle Korver gave a look of pleasant surprise. Guard J.R. Smith yelled out, “We got an [expletive] squad now.” And before James hit the locker room door, former NBA great Kevin Garnett hugged him and said, “Y’all look so different.”

It was just Game 1 with newcomers George Hill, Rodney Hood, Jordan Clarkson and Larry Nance Jr. in a Cavaliers uniform. But after a 121-99 rout of their fellow Eastern Conference power Boston Celtics, James, Altman and the revamped Cavaliers finally had reason to smile again.

“At the end of the day, I like being around guys that want to win and work hard,” James said. “I know I demand a lot of excellence in my teammates. I demand it out of myself too. On the road, we are going to play as well as we can and put ourselves in contention to compete for another championship. And that’s my mindset.”

The Cavaliers entered the 2017-18 season with legitimate title hopes after advancing to three straight NBA Finals — and that was even with All-Star guard Kyrie Irving being traded to Boston, per his wish. The Cavaliers still had four elite stars on their roster in James, Love and newcomers Isaiah Thomas and Dwyane Wade.

But on Feb. 6, the sky seemed to be falling for the Cavaliers after they blew a 21-point lead en route to an embarrassing 116-98 loss to the struggling Orlando Magic. Thomas, who missed the first part of the season while recovering from a hip injury, had not regained his All-Star form and voiced his displeasure off the court. Love is sidelined until late March with a left hand fracture. Wade wasn’t the old “D-Wade” anymore. James and Thomas didn’t see eye to eye on or off the court, sources said. And it was at that point that Altman and the Cavaliers, according to a source, decided it was time for major change to salvage a season with suddenly questionable title hopes.

Coach Tyronn Lue acknowledged that the Cavaliers had a bad spirit before the newcomers’ arrival.

“It was because of the losing. It wasn’t because of the guys,” Lue said. “Your spirits are always going to be down from losing.”

Said James: “Obviously, the last couple of months haven’t been what we expected.”

The Cavaliers were already in talks with the Los Angeles Lakers about Clarkson and with the Sacramento Kings about Hill but worked behind the scenes to make bigger moves on NBA trade deadline day, a source said. After the Cavs lost to Orlando, the Clarkson trade talks grew into something much bigger. In the first big move on Feb. 8, the Cavaliers acquired Clarkson and Nance from the Lakers for Thomas, forward Channing Frye and a protected 2018 first-round pick.

The Thomas era was over not long after it started. Meanwhile, young and talented Cavaliers newcomers Clarkson and Nance were excited to go from no playoff expectations to NBA championship expectations.

“You’re out there on the floor for a purpose,” said Clarkson, who heard about the trade after the Lakers’ brass woke him up from a nap. “You’re out there to win. I know we have one goal, I know [James] has one goal, and that’s to win that ‘chip.’ We’re just here to help do our job.”

Nance, an Akron, Ohio, native, said: “At first I was like, ‘Whoa, I got to move somewhere, like tomorrow.’ I was kind of shocked. I didn’t really expect it coming. But as the day went on, I got more and more excited about the opportunity.”

Hill was excited about the rumors about being traded to the Cavaliers but made a point to temper his excitement until it was officially completed. The addition of Hill brings Cleveland a veteran guard with 80 career playoff games who is defensive-minded with long, menacing arms, was the NBA’s top 3-point shooter, is outstanding in defending the pick-and-roll, has no problems voicing his opinion to James and every other teammate in a constructive way, and is still productive without the ball. With two more years left on his deal, Hill could also solidify Cleveland’s point guard position after the void left by Irving and Thomas.

Late on the morning of Feb. 8, Cleveland acquired Hill from the Kings for guard Iman Shumpert as part of a three-team trade. And once a gleeful Hill got the call that the trade was done, he instantly engaged in a victory lap while holding his infant daughter.

“I had a newborn daughter a month ago,” Hill said. “I had my daughter in my arms, feeding her a bottle because she was a big, chunky baby. And I get the call from my agent. I lifted the baby in my arms and ran around the house, not out of disrespect but out of excitement for a new opportunity.”

Equally as excited was James.

“George Hill’s basketball IQ complements me,” James said. “The guy has been in so many big games. You can tell he knows how to play the game smart. [He’s] big, physical, so we’re definitely going to work well together.”

The Cavaliers also acquired Hood from the Utah Jazz in the three-team trade that sent forward Jae Crowder to the Wasatch Range. Meanwhile, the Cavaliers also did Wade a favor by dealing him from a team suddenly deep in guards to his beloved old club that he probably never should have left, the Miami Heat. The Cavaliers traded Thomas, Crowder, Frye, Shumpert and Wade, all on Feb. 8.

Cavaliers forward Jeff Green called his agent just to make sure he wasn’t next before the 3 p.m. EST trade deadline arrived.

“It was crazy. I’ve been part of a trade …,” Green said. “That was crazy. My wife and I were sitting in the house and I was packing because we had a road trip. And I remember going to my bag and I came back, turned on the TV and it was the first trade, Isaiah. Damn. ‘Let me text Isaiah.’ Then I got up and walked away for two minutes and [ESPN’s Adrian] Wojnarowski was talking about the I.T. trade and they said, ‘Welp, we got another one for Cleveland.’ Then two seconds later, it was D-Wade. And then I text and said, ‘Who’s next?’ because you never know.

“It was something that happened quick. It was crazy. But I’m happy with the guys we had. I text my agent Roger Montgomery and said, ‘What the hell is happening?’ He said, ‘It’s been crazy. But I think you’re good.’ By this time, it was almost 3 o’clock, so let’s get in this car and go to the plane.”

Instantly, Hood, Hill, Clarkson and Jordan went from rebuilding situations to playing alongside a title-seeking James. The Cavaliers practiced on Feb. 10 and entered the Celtics game with just a few offensive sets in hand as Lue hoped to keep it all simple. Making the spotlight even brighter was the Celtics-Cavaliers matchup being featured nationwide on ABC as former Celtics great Paul Pierce had his No. 34 jersey retired.

Hood has played in 227 career NBA games, but he was “definitely nervous” about his Cavaliers debut.

“I was excited about getting to play for a championship and getting to play with LeBron,” Hood said before the game. “He is the best player of our generation. And to learn from him and play with these guys could further my development.”

If the new-look Cavaliers were nervous, unprepared or overwhelmed, you couldn’t tell. James told his teammates before the tipoff to play loose and play hard and not to worry about mistakes.

The Celtics owned a 32-31 lead through the first quarter. But the Cavaliers took over Paul Pierce Day by outscoring Boston 90-67 during the last three quarters. Hill calmly orchestrated the offense and nailed all four of his 3-point attempts. Hood added 15 points and three 3-pointers. Clarkson scored a bench-high 17 points and celebrated after nailing his three 3-pointers by holding three fingers to the hardwood as he ran down the floor. And Nance Jr. — like his father, a former Cavs star — dribbled down the lane for a replay-worthy dunk and enjoyed an alley-oop slam. James added 27 points, while the Cavaliers’ defense limited Boston to 40.4 percent shooting from the field and 26.8 percent shooting from 3-point range.

Basketball was fun again for James and the Cavaliers.

“Man, it’s almost like the new guys had been here,” James said. “It started with George, his on-the-ball pressure and just running the team. And then the three guys came off the bench. Jordan can score at any given time, but his composure was great. Rodney played with so much poise. And Larry was just controlling the perimeter by setting great pick-and-rolls, got him a lob, got a dunk. It’s a good start for the new guys. It’s a good start for all of us with our revamped team.”

Lue said it was a “good sign” that the newcomers played well in a “big game.” He also added that the “spirit was different” on this day and he was confident the Cavaliers would compete and play hard.

“They played hard. They competed. It was just good to see our team smiling again and having fun,” Lue said.

The Cavaliers do not have much time to practice before the playoffs begin in April. Cleveland will have only one practice before next weekend’s All-Star break and will have to lean on future shootarounds to get time in. Green said the key is getting healthy and understanding each other and getting better as a team for the long term.

The odds are typically against NBA teams having major success after making one big trade at the deadline, let alone adding four new key players. But if the new-look Cavaliers’ debut is any indication, there is much more reason for optimism now than after that Orlando loss.

“It was great. We were just having fun and enjoying the game again. When you win, that happens. When you lose, it doesn’t matter what type of group you have, you’re still going to be down. Just playing well, each guy cheering for another guy. It was just good to see tonight,” Lue said.

Said James: “We are going to play every other day, especially after the [All-Star] break. We have an opportunity to watch a lot of film, and when we do get on the floor, just go over what we do every night. We got some smart guys who came to our team who picked up some things very quick in yesterday’s practice and today’s shootaround. That’s a good start.”

The elephant in the room for Cleveland is that James can become a free agent this offseason and could depart his home state. The bold moves that Altman made, however, give Cleveland a much better argument for the four-time NBA MVP to stay. Keep in mind that the Cavaliers still own the struggling Brooklyn Nets’ first pick in the 2018 NBA draft. So even if James departs, Cleveland could still have a respected roster with Hill, Hood, Love, Clarkson, Nance, Smith, Korver, center Tristan Thompson, intriguing rookie forward Cedi Osman and a high selection in an upcoming draft that is top-heavy in impact talent.

Who knows what the future holds for James? But at least with this restructured, younger, athletic, talented and hungrier roster, the three-time NBA champion appears to have a renewed opportunity to compete for another title.

“The guys that are here are excited about this opportunity,” James said. “It’s my job to keep them excited about being here.”