BOSTON - The Boston Celtics have tied up the NBA finals, and they owe it more to “Big Baby” than the Big Three.

Backup Glen “Big Baby” Davis scored half of his 18 points in the fourth quarter on Thursday night as the Celtics bench pulled away from the Los Angeles Lakers to win 96-89 and even the best-of-seven series at two games apiece.

“Just will, that’s all it is,” Davis said. “This is what legends are made of, this is where you grasp the moment. ... Just play in the moment.”

Kobe Bryant scored 33 points and Pau Gasol had 21 for the Lakers.

Game 5 is Sunday night in Boston. The Celtics’ win guaranteed them a trip back to Los Angeles and averted a 3-1 deficit that has never been overcome in NBA finals history.

“We know what to do. We know how to play. We know how to get it done,” Gasol said. “And we know how important Game 5 will be, so we’ve just got to get ourselves mentally and physically ready ... to accomplish our mission.”

Paul Pierce scored 19 points, Kevin Garnett had 13 and Ray Allen bounced back from a seven-quarter shooting slump to score 12 points for Boston. But the new Big Three that led the Celtics to their unprecedented 17th NBA title in 2008 — beating the Lakers in the finals — was on the bench for much of the fourth-quarter run that gave Boston the lead for good.

And that was fine with them.

“I don’t think guys really care and that’s why we’re here, it really is,” Celtics coach Doc Rivers said. “(Rajon) Rondo and the rest of them, they were begging me to keep guys in. ‘Don’t take them out! Don’t take them out!’ It was great. That’s the loudest I’ve seen our bench, and it was the starters cheering from the bench.”

Boston’s starters were back in the game when Bryant scored 10 of the Lakers’ last 12 points, hitting all three free throws to make it 92-86 after he was fouled attempting a 3-pointer with 1:08 left. But then Rondo stole a pass from Bryant and took it the length of the court for a layup that made it an eight-point lead with 32 seconds left.

And this time, the reserves were cheering for the starters.

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“All I’m thinking about is, ‘Let’s win,’ ” Davis said. “I’m not thinking about anything else. I’m not even thinking about Kobe making all these shots, worried about this or worried about that. I’m just worried about winning, whatever it takes to win, and just making sure that I give my teammates positive energy to finish out the game.”

Bryant hit three straight 3-pointers to give the Lakers a 62-58 lead with 1:25 left in the third. Davis’ putback left the Celtics trailing by two points heading into the final quarter, and he scored on a reverse layup in the opening minute of the fourth to tie it.

Gasol made a basket to give L.A. the lead — its last of the game — before Allen scored, Davis followed, Allen made another basket and Davis followed with a three-point play that made it 71-64 with 8:22 left.

“They got all the energy points, the hustle points, second chance points, points in the paint, beat us to the loose balls,” Bryant said. “I mean, that’s how the game turned around.”

In all, the Celtics scored 13 of 15 points during a five-minute span when Allen was the only starter on the court, mostly with Davis, Rasheed Wallace, Nate Robinson and Tony Allen. Asked if he was surprised to see his bench extend the lead, Rivers said: “I’m happy. I don’t know about surprised.”

“We’ve done that during the season, but this is the finals,” Rivers said. “So it’s obviously different against such a quality team.”