BOSTON, Feb. 24 (Ticker) -- Down the stretch, the Boston Celtics could not stop the Houston Rockets' backcourt of Steve Francis and Cuttino Mobley

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Francis, who was battling a sore lower back, and Mobley combined for 20 of their team's final 22 points as the Rockets rallied from a late 15-point deficit to defeat the Celtics, 101-95, in overtime.

With the victory, the Rockets moved one-half game ahead of Phoenix, which lost at Chicago, for the eighth and final Western Conference playoff berth.

Francis collected 33 points, nine rebounds and nine assists and Mobley added a season-high 31 points and 10 rebounds for the Rockets, who have beaten the Celtics a franchise-record five straight times. Houston has not lost to Boston since November 22, 2000.

"It's the same way it was before the game, a little sore," said Francis of his back, which caused him to miss his team's victory over Memphis on Saturday. "My team really needed me and I thought I stepped up and played a really solid game against a good team tonight."

Houston trailed, 83-68, with seven minutes to play and by seven points with just under 3 1/2 minutes left before Mobley sandwiched a pair of 3-pointers around a three-point play to even the contest, 88-88, with 1:29 left.

"We decided to take it on (in the fourth quarter)," Mobley said. "It was a sense of urgency. We were concentrating on our shots and playing hard (defense)."

"Cuttino was phenomenal," Rockets coach Rudy Tomjanovich said. "He's been repositioning and in those situations and this time he let (the shots) fly. Big, big shots."

Neither team scored again in regulation, with Boston's Paul Pierce rimming out a jumper just before the buzzer.

The Rockets switched to a zone defense for the first time with 9:53 left in the fourth quarter after Antoine Walker connected on a 3-pointer that gave the Celtics a 79-66 lead. Boston shot 4-of-20 thereafter.

"That was our last resort because they were scoring to easy in the man," Mobley said. "They were getting too many second-chance shots, so coach changed it up, went to a zone and we became successful with it."

"It definitely slowed us down," Pierce said. "We stood around, we didn't really get enough movement. We shot the threes, but the game shouldn't have even gone to overtime. We had the lead in the fourth quarter and we let it get away. We took the shots they gave us instead of going for the shots that we wanted."

Houston took the lead for good, 95-93, on a 3-pointer by Mobley with 1:40 remaining. Rockets rookie Yao Ming nailed a pair of free throws and Boston's Tony Battie made a layup before Francis sank two from the line with 20 seconds left to give Houston a 99-95 edge. The All-Star point guard capped the scoring with a breakaway dunk in the final seconds.

Yao, a leading candidate for Rookie of the Year, attempted only two shots and finished with nine points.

"They were double- and triple-teaming the big fella and as much as we wanted to get him the ball, I think he understood because they had so many hands, arms and legs on him that we didn't want to force the ball into him," Francis said. "We moved the ball around and we were real patient tonight with our shot selection."

"They did a tremendous job (on Yao) in front and in back, switching guys on different plays," Tomjanovich said. "Our guys were trying (to get him the ball) and it was getting frustrating to get it in there."

Walker contributed 22 points and 11 rebounds, Pierce scored 22 points and Battie added 20 for Boston, which fell to 77-35 all-time against the Rockets.

"We blew a big lead, opportunity at home to get a big win," Walker said. "Up nine, 10, 12 in the fourth quarter with eight minutes to go. I was very disappointed."

The Celtics fell one-half game behind Philadelphia into fifth place in the Eastern Conference playoff race.

"We wanted to come in and protect our home court and stay on top of the four spot (in the playoff race) and we let it slip away," Pierce said. "No way, being at home, we should have given up that type of lead."

Houston limited Boston to just 37 percent from the floor (34-of-91), including 29 percent from the arc (10-of-35). The Celtics shot just 6-of-23 in the fourth quarter.

"(They were) not great shots," Celtics coach Jim O'Brien said. "I would like to see a little bit more penetration, instead of sometimes just passing it on the perimeter. But our team knows that Yao is waiting for them at the basket.

"(We) didn't get the opportunities we were getting in the first three quarters. That's life in the NBA."