BOSTON, (Reuters) – The Boston Celtics finally  overcame a determined challenge from the Chicago Bulls with a  109-99 victory on Saturday, the NBA champions edging their  enthralling Eastern Conference first-round series by a 4-3  margin.

Ray Allen scored 23 points and Paul Pierce had 20 for the  second-seeded Celtics, who will face the Orlando Magic in the  conference semi-finals which start in Boston on Monday.

“We turned into the Celtics again,” Boston coach Doc Rivers  told reporters after the Game Seven win.

“We started playing defense, getting stops.”

The seventh-seeded Bulls, who were led by Ben Gordon’s 33  points, forged a four-point advantage after the first quarter  but the Celtics clicked into top gear in the second with a  29-11 domination to race ahead for good.

“We weathered their storm and just hung in there,” Rivers  said. “Finally in the second quarter, we made a run.”

A 22-2 spurt consumed the final eight minutes of the second  quarter and enabled Boston to go from a six-point deficit to a  52-38 lead at the half.

Chicago never regained the lead although the Bulls pulled  within three points with 5:39 to play.

Boston, however, outscored Chicago 7-2 over the next three  minutes to put themselves in position to wrap up a thrilling  best-of-seven series which featured four overtime games.

“We just could not make enough shots to put any real  pressure on then,” Bulls coach Vinny Del Negro said.

Derrick Rose added 18 points and Kirk Hinrich had 16 for  the Bulls, who got 15 rebounds from Joakim Noah.

Kendrick Perkins supported the scoring of Allen and Pierce  with 14 points and 13 rebounds. Eddie House (16 points) and Glen Davis (15) also were in  double figures for the Celtics, who will face NBA rebounding  leader Dwight Howard of the Magic in the semi-finals.

“We definitely got our work cut out,” Pierce said of the  best-of-seven series. “But we are still the champs until  somebody knocks us off.”