Boston ? When their teams were among the best, Boston and Philadelphia had a rivalry as intense as any in the NBA.

With the Celtics back in the playoffs after a six-year absence, this old feud returns to Boston today for the start of a best-of-five series.

“These players were not around when the rivalry was developed,” said Celtics coach Jim O’Brien, who grew up in Philadelphia and went to college at St. Joseph’s. “I hated the Boston Celtics with a passion, and I loved Philadelphia just as passionately. I would literally sob every time the Celtics beat Philadelphia in the playoffs. I can still feel that.”

And does he still have feelings for the Sixers?

“No,” he said, cracking a smile. “I will not sob if Philadelphia were to lose the series.”

Bill Russell and Wilt Chamberlain met three times in the playoffs before the Philadelphia Warriors left for San Francisco. Then the Celtics played the Sixers five times in the 1960s including the ’65 division finals when John Havlicek stole an inbounds pass to seal a Game 7 victory.

Boston won 10 of 11 NBA titles from 1959-69; the other, in 1967, was won by Philadelphia.

With Larry Bird and Julius Erving, the teams renewed the rivalry in the early ’80s, meeting in the Eastern Conference finals four times. But it was in a game in early November that the tension boiled over and the two All-Stars brawled, grabbing each others’ throats before they could be separated.

“Whoever happens to be your opponent at the time becomes the rival,” said Red Auerbach, who’s spent more than 50 years in Boston as coach, general manager and resident sage. “Philly was in our division and we played them a lot of years in a row, so that was a little extra special.”

This may not have the intensity of the old rivalry, but there are still plenty of angles.

Reigning league MVP Allen Iverson missed the last 14 games of the season after breaking his left hand when Boston’s Tony Battie swatted at him on a drive to the basket. Iverson had a cast removed last week and was cleared to begin shooting on Friday, but he hasn’t taken part in a full practice .

The Sixers said it will be decided on the morning of the game whether Iverson plays.

Iverson led the NBA in scoring average with 31.4 points. But Boston’s Paul Pierce, who played in all 82 games, led the league with 2,144 total points.

“I’m aware of (the rivalry). I watched a little growing up,” Iverson said this week. “I don’t know if it’s going to be special. Hopefully it will bring some memories for the fans.”

Among those fans are “hundreds” of O’Brien’s friends and relatives. He grew up as one of eight children, with 17 aunts and uncles, many of whom still live in the Philadelphia area.

They know better than to ask for tickets.

“I made it known from the beginning of my coaching career that I was not in the ticket business,” he said. “I can assure you, I will not be distracted from what I will be doing.”

What he is doing is trying to win in his first playoff appearance as an NBA head coach, and then, maybe, earn Boston’s 17th NBA title.