LOS ANGELES — Paul Pierce looked up at the scoreboard and flexed his arms in triumph.

The Boston Celtics had erased an unprecedented deficit and beaten the Los Angeles Lakers 97-91 in Game 4 of the NBA finals today, moving one victory from their 17th league championship.

The longest-tenured member of the Celtics, Pierce lived through two failed rebuilding efforts before last season's overhaul that teamed him with fellow All-Stars Kevin Garnett and Ray Allen in a modern-day Big Three.

Now they have a chance to win a title — Boston's first since the original Big Three of Larry Bird, Kevin McHale and Robert Parish.

Pierce scored 14 of his 20 points in the second half, when the Celtics erased most of a 24-point deficit. He also guarded Lakers star Kobe Bryant, holding the reigning NBA MVP to 17 points on 6-of-19 shooting.

"Paul came to me at halftime and said, 'I want to guard Kobe. Let me guard him,"' Celtics coach Doc Rivers said. "I think people will look at his offense, but I thought we won the game because Paul was a tremendous defensive player tonight."

Garnett had 16 points and 11 rebounds, Allen had 19 points and nine rebounds, and reserve Eddie House scored 11 points, nine in the second half, including a baseline jumper with 4:07 left to give Boston its first lead of the game, 84-83.

"We said, 'We can win this game, and we're going to win this game,"' said House, who had a masseuse rub down his shoulders at halftime. "I think everybody had the belief that we're going to win this game and it was our game to win."

The Celtics trailed by a record 21 points after the first quarter. No team had ever overcome a first-quarter deficit of more than 15 points in the NBA finals and won.

"We said we weren't going to back down," Pierce said. "At the end of the third quarter, I looked up at the scoreboard and told the fellas, 'We just have to go out there and compete and let the chips fall where they may."'