SAN ANTONIO (AP) -- Coach Doc Rivers had some strong advice for the Boston Celtics before their first stop on a tough three-game swing through Texas: Play hard, or else.
"The Spurs, they're a well-oiled machine. We knew they were going to come in fired up. They lost some games as of late and any champion is going to come out with its haymakers," said Kevin Garnett, who had 21 points in Boston's 93-91 win over the San Antonio Spurs on Monday night. "Doc told us if we don't pick up the energy, then we're going to get embarrassed in here."
And for the first two quarters, anyway, it looked like that might happen.
The Spurs led by as many as 22 points in a lopsided first half before Boston rallied for a narrow victory.
"A lot of teams may have buckled," said Rajon Rondo, who scored 20 points for the Celtics. "But we knew we had to execute. Continue to get stops on defense and we knew the game would change for us, and it did."
Veteran guard Sam Cassell had 17 points and gave Boston its first lead of the fourth quarter with 46 seconds left when he hit a 3-pointer to make it 89-87.
"He's got a lot of experience. That's why we brought him in," Pierce said of Cassell. "Late in the game, that's what he does, he knocks down the big shot that puts us up two. That's what you can expect from him."
San Antonio trailed 93-89 after Eddie House hit two foul shots for Boston to make it a two-possession game with 9.6 seconds left. Parker then got an easy basket for San Antonio but it appeared too late for the Spurs. But with two seconds -- and a timeout -- left Bruce Bowen stole the ball from Garnett on the inbounds play and passed to clutch-shooter Robert Horry, whose 3-point attempt missed. Horry sank to the ground, his head in his hands.
"It would have been good if one of them called timeout probably," Spurs coach Gregg Popovich said. "But in the heat of battle that doesn't always occur to you."
Horry said that was exactly what happened.
"You've got so much adrenaline going -- you've got a steal -- you're not even thinking about timeout," Horry said. "I saw five guys coming at me and I threw it up."
The Spurs have now lost six games at home this season. Their last home loss was Jan. 26 against the New Orleans Hornets.
"I'm just mad that we had a 22-point lead and blew it," Horry said. "We shouldn't have even been close. We should have done what we were supposed to do and won this game, especially at home and you're up 22. I don't care who you're playing."
The Spurs led 70-68 after three quarters and extended the lead to 79-72 on Horry's 3-pointer with 8:04 to play. Duncan soon followed with a pair of highlight blocks against Pierce and House before Pierce led a 9-2 run by the Celtics to bring Boston to 83-81 with 3:11 left.
House's first points of the game -- a 3 from the corner -- made it 85-84 Spurs with less than two minutes to go.
Cassell then hit another 3 -- this time from the top of the arc -- to give Boston the lead. Rondo grabbed a key offensive rebound for the Celtics between Bowen and Parker and hit two from the line with 16.6 seconds left to make it a two possession game.
The Spurs missed a chance at a 3-point play when Ginobili was fouled by Pierce but his layup rolled all the way around the rim before going out. Ginobili hit both from the line to bring the Spurs within two with 11 seconds to go.
After being dominated by the Spurs for the opening two quarters and trailing by 10 at the half, 53-43, the Celtics opened the third with a 17-4 run to take their first lead of the game, 56-55, off Pierce's easy fastbreak dunk with 8:24 on the clock.
Rondo had 12 points in the period -- including eight straight -- for Boston, but the Celtics couldn't build more than a three-point lead and were down two points with a quarter to play.
Ginobili, the Spurs' leading scorer, returned to the reserve role he's had most of the season after starting all but two games since Jan. 29.
The Celtics take on the Houston Rockets and their 22-game winning streak on Tuesday, but Rivers said pregame he wasn't thinking about that just yet. "To me they're [the Spurs] still the team to beat no matter what the streak is, or what anybody's streak is. ... History tells us we should focus on the Spurs." ... Rivers said he doubted Allen would be ready for Houston, saying Thursday's game vs. Dallas is more likely. ... This is the second straight year the Spurs and Celtics have played on St. Patrick's Day. Boston won last year, 91-85, beating the Spurs in San Antonio for the first time since Feb. 14, 1990. ... Spurs G-F Ime Udoka was back after sitting out two games with tarsal tunnel syndrome in his right ankle. ... The Celtics' 11 first-quarter points were a season low.