ATHENS, Greece — Before the hard part begins against Spain, Tim Duncan and the U.S. basketball team got to experience a taste of what the good ol' days were like at the Olympics.

Finally playing an opponent they were able to handle with ease, the Americans finished off the preliminary round with an 89-53 victory over Angola Monday.

With the quarterfinals coming up Thursday, Duncan believes the worst is already in the past.

"I'm really confident in the way we've been playing," he said. "I think we've learned a lot through this tournament, and I think we're in a great position."

The Americans had to wait until Greece defeated Puerto Rico 78-58 in Monday's final game to find out their next opponent, Spain (5-0). China earned the final medal-round spot from Group A by upsetting Serbia-Montenegro 67-66 behind 29 points from Yao Ming.

The other quarterfinal matchups will be Greece-Argentina, Puerto Rico-Italy and China-Lithuania.

The United States finished the opening round 3-2, losing to Puerto Rico and Lithuania, and defeating Greece, Australia and Angola. Under point differential tiebreakers, the Americans finished fourth in their group behind Greece (3-2) and Puerto Rico (3-2).

"We wish we could have won some more and played better against Lithuania and all that good stuff, but we didn't and we're in the position we're in right now, and we're happy with where we're at," Duncan said.

After a series of tough games in which he was constantly doubled-teamed, the 7-foot center finally found some room to maneuver against Angola.

In the opening moments of the first quarter, he found just one defender guarding him, and he gladly took advantage, dropping in a shot.

Duncan finished with a team-high 15 points in just 13 minutes, and the Americans dominated the boards Barcelona-style with a 52-17 edge in rebounding as NBA commissioner David Stern watched from a seat 10 rows behind the American bench.

Shawn Marion took the U.S. team's first 3-point attempt 82 seconds into the second quarter and made it for a 28-14 lead, and LeBron James hit another 3 to extend it to 33-14. The U.S. team finished 3-for-6 from behind the arc and 33-of-60 (55 percent) overall.

"The only negative, I thought, was we turned the ball over a lot (12 times) in the first half, which has plagued us a lot in this tournament," coach Larry Brown said.

The Americans were up 46-26 at halftime before Duncan scored their first six points of the third quarter. An alley-oop reverse layup by Richard Jefferson off a pass from Allen Iverson got the lead up to 30 less than four minutes into the second half.