The separation was obvious last season when the Golden State Warriors came to Boston. On one side of the locker room, Baron Davis and Monta Ellis studied film together. On the other, Andris Biedrins and Mickael Pietrus compared game notes. In the middle, Patrick O'Bryant sat at his locker. Alone.

By now it's no secret that O'Bryant was a never a fit for Don Nelson's Warriors squad. His style of play didn't mesh with the coach's up-tempo system. In just two disappointing seasons, the former first-round pick from Bradley was dubbed a bust.

"The way I grew up playing was more inside-out type of playing," O'Bryant said this week at the Celtics Media Day. "I went to Golden State and Nellie had a different system and it wasn't really for me."

Initially the Boston Celtics signing of O'Bryant raised concerns. But after averaging less than two points and two rebounds per game last season, the seven-footer is already a key piece on the team. He is the only true center available now that Kendrick Perkins has been shelved from exhibition games to recoup from offseason shoulder surgery.

"I just don't want it to happen again, especially during the season," Perkins said of his injury. "I'm not really too concerned going into training camp. The season is more important."

Perkins's nagging shoulder has bolstered O'Bryant's status from a disposable bench warmer on the Warriors to a potential preseason starter on the world champion Celtics.

"[I'll bring] some help down the post on defense," O'Bryant said. "Perk's only one guy. He can't do it all himself. I'm hoping to help back him up and block some shots and get some rebounds."

O'Bryant spent the second half of his summer working out with Celtics assistant coach Clifford Ray at Ray's Big Man Camp in Florida. Ray stressed the importance of hustle, energy and conditioning, and expectations for O'Bryant ran as high as three blocks per game. Sources noted that O'Bryant tried to shake a lingering two-guard mentality from his days with the Warriors and develop a stronger game down low, which already includes a sky hook.

"[Coach Ray taught me an] understanding of the post game, the way that Doc (Rivers) wants to run it here in Boston," O'Bryant said. "He helped me out with a lot of stuff like that and he told me what Doc will expect from me for me to stay on the court here."

The first test for the 22-year-old will come next Wednesday when the Celtics open their exhibition schedule against the Philadelphia 76ers. He has made strides in his first week of practice and already has a vote of confidence from Perkins.

"Patrick's a great guy," Perkins said. "He comes in, he's willing to listen, he asks questions, and he's a great player. I think Patrick will help us a lot. He'll give us athleticism and I think he's a good addition to our team."

After two forgettable seasons on the West Coast, O'Bryant agrees.

"I couldn't ask for any better situation," he said. "They're the defending world champs. You've got great players with Paul (Pierce) and KG and Ray (Allen) and everybody here, and it's an offense more suited to my style."

When the Golden State Warriors come to Boston this season, don't expect O'Bryant to be sitting alone at his locker again.

Jessica Camerato covers the Celtics for WEEI.com.