Boston Celtics swingman James Young is a reminder of just how fast things can change in the NBA.

Three weeks ago, the Celtics would have bid farewell to the former first-round pick if another team had offered anything of value for him in advance of final roster cuts. Even after winning the team's final roster spot, Boston declined the fourth-year option on Young's rookie contract, valuing a tiny sliver of future cap flexibility over the guarantee of bringing him back next season.

But on Saturday night, with the injury-depleted Celtics playing the second night of a back-to-back on the road against the Indiana Pacers, coach Brad Stevens called Young's number early in the second quarter. He responded with what was unquestionably his finest all-around effort at the pro level.

From diving on the floor for loose balls to hitting open 3-point shots to aggressively driving at the basket, Young put up 12 points on 5-of-6 shooting over 16 inspired minutes as part of Boston's 105-99 triumph over the Pacers at Bankers Life Fieldhouse.

"I told James to be ready [Friday against the Knicks]. He never got in when it was still a game, but I told him one of the next two games he'll probably be really impactful," Stevens told reporters in Indiana. "He's shot it at such a different level than he shot it two years ago when he got here, as far as accuracy in workouts, in practice, and everything else. He's certainly always a capable shooter with a beautiful stroke, but he's really really worked hard on becoming accurate. He either shoots it or moves it and I thought, with that group, that was a good thing."

James Young's 12 points off the bench were crucial in Saturday's victory over the Pacers. Trevor Ruszkowski/USA TODAY Sports

"[Defensively] I thought he was just active. We need him to be active, long, and physical."

Young, who had been scoreless in 18 minutes over Boston's first eight games, replaced rookie Jaylen Brown early in the second quarter with the Celtics down eight. Shortly after entering, Young and fellow 2014 draftee Marcus Smart denied an entry pass to Pacers big man Myles Turner and, when the ball squirted loose, Young laid out to force a jump ball.

The hustle sequence seemed to settle Young, who drove hard at the basket for an off-balanced layup on Boston's next possession. Stevens went back to Young midway through the third quarter and rode him for a key 10-minute stretch in which the Celtics took a lead they wouldn't relinquish. In the final moments of the third quarter, Young had both a dunk off a pretty feed from Isaiah Thomas and a go-ahead 3-pointer that sent Boston into the final frame up three.

During an on-court interview with Comcast SportsNet after the game, Young said of his performance, "Just play hard -- that's all I could do. I didn't want to do too much but yet stay composed and play my game. ... I thought we needed to be a little bit more energetic on defense, and that's what I tried to do."

It's an incredibly small sample but, in 35 minutes of total floor time, Young owns the best defensive rating on the Celtics' roster, with the team giving up a mere 88.5 points per 100 possessions. For context, that's 18.7 points per 100 possessions lower than Boston's cringeworthy season average. Young clearly has bulked up the past three years and can now hold his own against NBA small forwards.

Still, Young is probably better regarded as an offensive player, even if he's still trying to prove he can consistently make shots at this level. Stevens has repeatedly raved about Young's newfound consistency behind the scenes. Young is often one of the final players on the court after practices, where he typically engages in shooting drills or 1-on-1 work with teammates.

Saturday's performance will encourage Celtics fans to dust off the "Young and Smart" T-shirts that the Celtics sold after the 2014 draft. Smart, the No. 6 pick that year, has elevated to the starting lineup with Jae Crowder (ankle) sidelined. Regardless of role, Smart might be the X-factor in Boston's success this season.

Young? The 21-year-old needed a solid camp to convince Celtics' brass to keep him over 2015 first-round pick R.J. Hunter. The additions of both No. 3 pick Brown and veteran swingman Gerald Green seemed to increase the competition for minutes at his position, but Young stated a strong case for minutes Saturday.

Few would have predicted that this week would end with Young earning Comcast's "Player of the Game" award for his contributions on Saturday. Before Saturday's game, Young's most noteworthy moments of the 2016-17 regular season were his fashion choices. An airbrushed jean jacket with a Pokemon on the back was an eyebrow-raiser earlier this week, while his two-toned Jordan 16s shoes were notable on Friday.

Crowder could be back next week and Brown is going to get every opportunity to develop despite his own growing pains. Young is going to have to fight to stay in the rotation. But if he can consistently impact games the way he did Saturday, he'll force Stevens to find a way to utilize him.