SAN ANTONIO ? The San Antonio Spurs fell back on their outstanding defense to win another world championship Thursday night.

The Spurs wouldn’t let the Detroit Pistons anywhere near their basket in the fourth quarter of Game 7, grinding out an 81-74 victory at the SBC Center to capture their third NBA title in seven seasons.

The score was tied at 57 after three quarters, but San Antonio slowly took over the game in the fourth. Its defense – which had been shredded by Detroit in Game 6 – clamped down on the Pistons’ two big scorers, Chauncey Billups and Richard Hamilton, while its offense knocked down three clutch three-pointers.

“I don’t know how the hell we did it,” Spurs coach Gregg Popovich said during the trophy presentation, “but I don’t care.”

Tim Duncan (25 points, 11 rebounds) was named Finals MVP for the third time, and the third ring gives him as many as Larry Bird and one more than Isiah Thomas. It was another brick in the wall for San Antonio, an organization that eschews glamour and glitz in favor of humility.

That the Spurs also have Duncan to build around doesn’t hurt.

He had been called out by many during this series because he had been good but not great, more than solid but not dominant. He was not always dominant Thursday, but he imposed his will on the game in the second half, getting the Pistons’ big men in foul trouble, hitting the glass and generally getting all of the action in the game to flow from him.

San Antonio's Manu Ginobili celebrates winning the NBA title. The Spurs beat the Pistons, 81-74, in Game 7 of the NBA Finals on Thursday in San Antonio.

“I don’t listen to anything that was said,” Duncan said. “I wanted to come out here and give my best effort. We fought for this thing.”

In the fourth, he set up Bruce Bowen for a three that gave the Spurs a 67-61 lead. After Rasheed Wallace – the only Piston to score during the first eight minutes of the period – hit a jumper, Duncan knocked down a baseline shot.

And after a Billups basket, Duncan’s post play set up another three. Manu Ginobili (23 points, four assists, five rebounds) spotted up for the trey with 2 minutes, 57 seconds left, giving San Antonio a 72-65 lead and sending the sell-out crowd into delirium.

“I am unbelievably happy. I couldn’t be happier,” Ginobili said. “It’s just an unbelievable feeling. I need another body to feel it.”

The Pistons, scrappy as ever, tried to rally, but never got closer than four points.

The Spurs’ win ended an amazing season for the Pistons, who defended their championship with heart, if not always skill. The brawl Nov. 19 at Auburn Hills, Mich., defined their season, as did coach Larry Brown’s seeming wanderlust for a job with the Cleveland Cavaliers during the playoffs. They were behind the Pacers in the second round of the playoffs and won; they were behind the Heat in the Eastern finals and won; and they were down by three games to two coming here after losing Game 5 at home.

But they couldn’t get over the last hump.

San Antonio's Tim Duncan (21) holds his MVP trophy, left, and the NBA Championship trophy. The Spurs won Game 7 against Detroit, 81-74, to win the championship Thursday in San Antonio.

Popovich had hoped for a fast tempo, and had said before the game that Duncan would get a lot more touches in Game 7 than in Game 6. Duncan did get up nine shots in the first half, but it was veteran Robert Horry who appeared more aggressive early, scoring 10 first-half points, mostly on strong drives to the basket.

And while the slow pace and hand-to-hand fighting helped Detroit keep the score close – there were 11 ties and nine lead changes in the half – the Pistons paid a price for the physical play. Both of their Wallaces, Ben and Rasheed, picked up two fouls before the halfway mark of the second quarter. Rasheed Wallace played just 28 minutes and finished with 11 points. Hamilton led the Pistons in scoring with 15.

But the Pistons got unexpected offense from Ben Wallace, who scored three straight times in the second quarter on dunks and hit six of his seven first-half shots from the floor. That helped Detroit to a 39-38 halftime lead; the 77 total points at the half were the lowest ever in a Game 7 of the Finals.

With the Pistons’ big men in foul trouble, Duncan began to assert himself inside. With his team down by 52-46 in the third quarter, he started another Spurs run with two free throws, then converted a three-point play the next time down. He scored 12 points in the quarter.

Brown, a Hall of Fame coach, has said if doctors deem him healthy enough, he wants to return next season with the Pistons. He insists he will not coach another NBA team.

“If I don’t come back, it’ll be for the right reasons,” Brown said. “A lot of people have a lot of worse things than me.”