The Philadelphia 76ers got an unexpected scoring boost from Caldwell Jones tonight and used it for the impetus to come from behind and beat Boston, 121-113, and gain a split in the first two games of the NBA Eastern Conference finals. The Celtics had romped, 121-81, in Sunday's opener.

Jones, a defensive specialist who averaged eight points a game in the regular season, scored eight straight points late in the fourth quarter and finished with 22.

"We matched base line jumpers with them for a while, Caldwell against Larry (Bird)" Boston Coach Bill Fitch said, shaking his head. "Caldwell hit nothing but net and Larry hit nothing but iron. That's one reason games are lost, the ball just won't go in."

The Celtics now have lost the home-court advantage and must play back-to-back games in Philadelphia Saturday and Sunday afternoons before returning here for Game 5 next Wednesday.

Coach Billy Cunningham said that one of his pregame plans was to try to get Jones more involved in the offense. Philadelphia's 7-foot-1 center scored six points in the first four minutes, but then didn't start shooting again until midway through the third period.

"I'm the designated hitter," Jones said, with a smile. "They don't call on me until they need me."

The 76ers had nudged in front, 105-100, when Jones went into his act. He was wide open on the left side when he hit his first 14-footer. On the next possession, Philadelphia ran the same play and he connected again. The play repeated with the same results and the 76ers were in front, 111-106, prompting Fitch to angrily wave for a timeout.

"Don't blame (Robert) Parish for all those shots," Fitch said. "A teammate called switch three times and then didn't get out and cover Jones. It wasn't one man's responsiblity."

When play resumed, Jones went into action again, this time with a sweeping running hook in the lane, which probably surprised even some of his teammates.

Andrew Toney, the game's top scorer with 30 points, then made a 15-footer and layup after a pass from Maurice Cheeks (14 assists) and the 76ers were in command, 117-108, with 1:47 to play.

"The game plan was to move Parish away from the hoop so they couldn't play team defense and help out," Jones said. "We wanted to make them play one-on-one defense."

Philadelphia took the first substanial lead, 18-13, but Bird scored six straight points and M.L. Carr made a breakaway layup to put the Celtics in front, 21-18.

Darryl Dawkins, who was replaced in the starting lineup by Bobby Jones, entered the game after eight minutes and scored seven points in three minutes to give the 76ers a 31-29 lead going into the second period.

After Cedric Maxwell's three-point play tied the game at 49, Philadelphia scored nine of the next 11 points. Toney scored nine points against Chris Ford in the last 4 1/2 minutes of the first half to help boost Philadelphia's lead to 62-56 at intermission.

There were 16 lead changes in the third period, which ended with the Celtics in front, 90-88, after Kevin McHale scored the last four points. Parish, scoreless in the first half when he picked up his third foul in the closing seconds of the first period, came back with 11 points in the third quarter.

Toney scored Philadelphia's first six points of the fourth quarter, but Nate Archibald answered with six of his own and the Celtics still led, 100-99. Clint Richardson made a 12-footer, Bobby Jones made two free throws and Richardson added a pair of foul shots to move Philadelphia in front, 105-100.

Then Caldwell Jones took over, just like he did when he scored 20 points in Philadelphia's sixth-game--and deciding--victory Friday night in Milwaukee.

"This is the way Philadelphia played against Milwaukee," Fitch said. "This is the way they're capable of playing, but they can play even better. It's going to be a hell of a series."