By Steve Keating

BOSTON (Reuters) - Paul Pierce gave Boston a scare when he left Game One of the NBA final with an injured knee on Thursday, but his return sparked the Celtics to a 98-88 win over the Los Angeles Lakers.

Boston's championship dreams looked set to become a nightmare in the third quarter when Pierce collided with team mate Kendrick Perkins and crumpled to the floor clutching his right knee.

The hushed crowd looked on as the Celtics captain and leading scorer was helped off the court and wheeled to the locker room in a wheelchair.

However, after testing the knee, Pierce made a dramatic return to the court to ignite his team, nailing key back-to-back three-pointers to help propel the Eastern Conference champions into a four-point lead over their old adversaries.

"When I first fell to the ground I heard a pop in my knee, and all I felt was pain when I grabbed it," Pierce told reporters. "At that point I thought I tore something.

"Once I felt I could put weight on it, I was like; I had to get back out there to help my ball club.

"That was all that was going through my mind, just being a part of it. I just wanted to get back out there.

"A lot was going through my mind, and I was like, man, it can't be over like this."

Pierce finished the night with 22 points after scoring just three in the opening half.

No one in the sold-out Garden was happier to see Pierce bound down the tunnel than team mate Kevin Garnett.

Garnett, playing in his first NBA finals, paced the Celtics with 24 points but said it was Pierce who turned the tide.

"We saw him being carried off and we didn't know what the situation was," said Garnett.

"When he came out, you just heard the roar of the crowd.

"He was walking, he was up on his own strength, and he rejuvenated us, I think to the point where he gave everybody life.

"I could tell that everybody was rejuvenated. It was good to see him be okay and in action."

(Editing by Peter Rutherford)