BOSTON -- Kyrie Irving looks different. He has just jogged off the Auerbach Center court after an informal pickup session with his Boston Celtics teammates and his distinctly more chiseled upper body is beaded with sweat.

He's sporting a headband to keep a fuller noggin of hair at bay, and he's smiling. A lot.

There's a simple reason for that: He's no longer in pain.

Last season, Irving gutted through persistent soreness and irritation caused by hardware from a 2015 surgery to repair a broken kneecap. He was forced to shut it down in March, underwent two additional surgeries, then spent much of his offseason methodically fine-tuning that left knee to the point where he believes he is the healthiest and strongest he's been in three years.

"I'm moving completely differently," Irving told ESPN on Friday, just days away from the official start of training camp. "I've worked on my strength and have a heightened awareness of what my body needs on a day-to-day basis. I spent all summer trying get my left leg to catch up with my right. And it's there."

Irving said he's ready to compete with no restrictions. His knee, he said, was tested during offseason runs in Seattle with Jamal Crawford and Zach LaVine, a Labor Day sojourn to the Bahamas with Jayson Tatum and Kevin Durant, and, in recent weeks, at Boston's new practice facility with his teammates.

"Our pickup games are next level," Irving said. "I mean, next level. You can't believe what we're doing out there. We can't wait to get started."

When the Celtics acquired Irving in August 2017, he and his agent, Jeff Wechsler, informed Boston that a tension wire from the 2015 operation was a source of pain for the point guard and would eventually need to be addressed.

"We told them all about it," Irving confirmed. "It wasn't a surprise."

He hoped to make it through the season, but finally succumbed to minor surgery to remove the tension wire in March, then needed a second, more serious procedure in April when pathology tests revealed a bacterial infection. Surgeons removed two screws from his left patellar tendon to clear the infection. That procedure left him hooked up to an intravenous line for the next six weeks.

Irving declared all of those issues behind him. He eschewed most offseason extracurricular activities to focus solely on his rehabilitation, and it has paid dividends. He claimed to have a confidence in his lower body that simply did not exist during his abbreviated 2017-18 season.

"Now when I go to the rim," Irving explained, "I'm able to maintain my strength and athleticism, so when I get under there I have all sorts of options. No limitations. I can pick my spots. It's a lot better."

Expectations are soaring for a deep Boston team that thrived on the defensive end last season but missed Irving's offensive artistry once the postseason began. When asked if it would be a disappointment if the Celtics didn't make it to the Eastern Conference finals in 2019, Irving firmly answered, "Yes."

Pressed if he would be disappointed if they didn't win a championship, Irving responded, "Can we beat Golden State in a seven-game series? Yes."

What makes him so sure?

"Because of who we have," Irving answered, "and what we're establishing here, not just for this season, but for hopefully for the next few years, something that's pretty special.

"I've played against Golden State in three straight Finals (2015-17) -- two that I was able to participate in -- and seeing them evolve, with the talent they have, and then adding DeMarcus Cousins [this offseason], it's like 'OK, the whole league is on notice.'

"But there's one factor that they're aware of, and I'm aware of, and that's that I've seen them up close. I've played them so many times. We've gone in a seven-game series [when he was in Cleveland], so I know what it takes.

"Now, how do I communicate to our guys that this is the top-tier team, and we have to grow immensely in the next six months to beat them consistently? Not just one game, not just two, but in a seven-game series, because they're so dang great. They're a powerhouse."

Irving said he's aware that he's been linked to Jimmy Butler in persistent free-agent rumors regarding a mutual desire to play together in New York, but he said he's had no such discussions with Butler. In fact, he said, the last time he talked to Butler at length was when they were both playing with USA Basketball, and the two engaged in a spitballing session along with Durant and Cousins about what the future held for each of them.

"And that," Irving laughed, "was in 2016."

"Who wouldn't be a part of this?" Irving said, gesturing to Boston's new practice facility. "Who wouldn't want to be a part of Jaylen Brown and Jayson Tatum and Al Horford and Gordon Hayward? People keep saying, 'Why won't he commit to Boston?'

"Well, there are financial implications involved."

If Irving had signed an extension with Boston this past summer, he would have potentially left more than $80 million on the table than if he waits and re-signs with the Celtics next summer.

"I'm accepting it's going to be a constant story," Irving shrugged. "It's a point in my professional career where it is a big-time decision. I've been away from Cleveland officially for a year now, and I'm finally getting acclimated in Boston.

"Last year it was almost like a trial. There was a lot going on. It was overwhelming at times, to be honest. The focus needed to be directed on getting better and helping my new team win a championship, instead of focusing on all the outside noise [regarding his departure from Cleveland] that affected me personally.

"I was afraid to admit that initially, because I wanted to be prideful and handle everything. So, it's been a matter of figuring it out and growing.

"It only affects me when it affects my teammates. I keep them abreast of everything. We need to be communicating like that, because there are very few years where you get a chance to be a championship team -- unless you are Golden State."

Irving acknowledged there is a logjam of talent at some positions on the Celtics roster and said healthy competition will only push them harder.

"The drive for greatness, the drive to win a championship, that's all I care about," he said. "The rest of it doesn't matter."