OAKLAND, Calif. -- The defending champions were drained -- and coach Doc Rivers suspected it might happen. The end of a 19-game winning streak can do that.
Stephen Jackson returned to the lineup and scored eight straight points during the decisive fourth-quarter stretch to finish with 28, and the Golden State Warriors sent Boston to back-to-back losses for the first time this season by rallying past the Celtics 99-89 on Friday night.
Paul Pierce had 21 points and five assists and Kevin Garnett scored 14, but the Celtics couldn't hold a 14-point lead a day after their franchise-record 19-game winning streak ended with a nine-point loss to the Lakers in Los Angeles on Christmas.
"I was worried at halftime when I saw we were shooting 56 [percent] and they were shooting 39 and it was a 12-point game," Rivers said. "I was completely concerned about it. ... Once they start making shots, it's tough to turn them off, and we couldn't make anything."
Boston (27-4) still must play at Sacramento on Sunday and at Portland on Tuesday to complete this West Coast swing before heading home. The Celtics dropped consecutive games for the first time since March 22 and 24 last season.
"They got hot late," Boston's Leon Powe said. "We had a chance to put them away but they were getting the loose balls and making some big shots."
Jackson -- who had missed the past four games with a sprained left hand -- scored 15 points in the final period and Marco Belinelli totaled 22 for the Warriors, who have won five straight and 12 of 15 against the Celtics at home. Golden State lost 119-111 in Boston on Nov. 26 in the teams' first meeting.
"We're looking for something to get us going. We're looking for something to turn things around," Jackson said. "This should give us some momentum and some confidence."
Kelenna Azubuike's 3-pointer with 7:47 to play cut the Celtics' lead to 76-74 before Ray Allen hit a floater on the other end. Jackson then scored eight straight points for Golden State. He followed Allen's bucket with a 3 at 7:03, hit the go-ahead basket with 6:02 to play to make it 79-78, then made another 3 at 5:33.
After Eddie House's 3 pulled Boston to 93-87 with 1:17 left, the Celtics had two misses and Jackson knocked down a pair of free throws with 36.2 seconds to go.
"I think we're all looking at ourselves in the mirror individually to see what we can do to get better, to make this team better," House said.
With Garnett and Rajon Rondo on the bench, Belinelli hit consecutive 3-pointers in the final minute of the third quarter for the Warriors, who trailed 72-64 heading into the final period. Ronny Turiaf dunked for Golden State to start the fourth, pulling his team the closest it had been since late in the first quarter and delighting the Warriors' second sellout crowd of the season.
Turiaf finished with 14 points and eight boards.
"We fired up in the fourth quarter -- just the way we drew it up," Warriors coach Don Nelson said. "As they go along in their journey in the NBA, they're going to have games when the other team gets hot at the wrong time and all of a sudden catches them off guard. So, it's probably no big thing to them but it's a very big thing to us."
Rondo had 11 points on 5-of-11 shooting, 10 rebounds and nine assists to go with seven turnovers. He shot just 3-for-11 against the Lakers for six points after scoring 26 and 18, respectively, in his two prior outings on a combined 19-of-26 shooting.
After Golden State pulled to 42-35 late in the first half, Allen answered with a 3 on the other end for his first points of the game and the Celtics led 51-39 at the break.
Boston was minus starting center Kendrick Perkins, who injured his left shoulder in the first quarter Thursday. Local standout Powe earned the start in Perkins' place and finished with 12 points and seven rebounds.
This marked Powe's first return to his native Bay Area in uniform since winning a championship. He was a college star at California and played his high school ball at nearby Oakland Tech. He was able to see some friends and family on Christmas night and planned to do some more visiting before leaving town. ... Boston plays on consecutive days 17 times this season, none of those at home. ... The Warriors played without G Jamal Crawford (strained left groin) and F Corey Maggette (strained right hamstring). ... Golden State G Monta Ellis, still recovering from ankle surgery after an offseason mo-ped injury, made his first appearance on the Warriors' bench -- albeit in street clothes. There is still no timetable for his return, though he has been working the past two weeks to regain strength in the ankle. "He's coming along nicely," Nelson said. ... New Yankees ace CC Sabathia sat courtside. The burly left-hander this month received a $161 million, seven-year deal -- the richest ever for a pitcher.