There were many times this season when it seemed unlikely Jermaine O'Neal would ever contribute. Dogged by knee injuries since training camp, O'Neal missed 58 games. He was an afterthought in the Celtics' postseason plans as recently as last month, when he spent three weeks rehabilitating in Chicago with renowned basketball trainer Tim Grover. Though most outsiders didn't expect O'Neal back, he never lost faith. "I think when you have doubt you never get where you're supposed to be," said O'Neal, who underwent surgery on his left knee in February. "If you challenge yourself and you can't get to that goal, then you have to be honest with yourself and just say, 'I gave it my all, but it didn't work for me.' But every week in Chicago I felt like I was getting ready to get back." That faith was rewarded last night, when O'Neal had 12 points on 6-of-6 shooting and four blocks in the Celtics' 87-85 win over the Knicks in Game 1 of their first-round playoff series. "We won the game because of Jermaine O'Neal," Celtics coach Doc Rivers said. "That's it. Forget his offense. His defense, his presence, his shot-blocking, his rebounding, his toughness — and he did it in both halves. He was absolutely wonderful." Starting in place of the injured Shaquille O'Neal, Jermaine sparked a pivotal third-quarter turnaround, scoring six points as the Celtics cut into a 12-point halftime deficit.