BUENOS AIRES, AUG. 17 -- Led by Drazen Petrovic's 31 points, most coming on three-pointers, the powerful Yugoslavian basketball team eliminated the United States, 99-91, in the semifinals of the World Basketball Championships today.

Petrovic, who plays for the Portland Trail Blazers of the National Basketball Association, frustrated and demoralized the young U.S. squad all afternoon with his sure ballhandling and his accurate jumpers. Whenever the U.S. team made a run, he was there to snuff it out with a steal, an assist or a three-point shot.

The U.S. team now plays Puerto Rico in a consolation round Saturday for third place. Yugoslavia will play Sunday in the finals against the Soviet Union, which got 26 points from forward Valeri Tikhonenko and survived a scare from the Puerto Ricans, 98-92, in the other semifinal game.

The Yugoslavs' clear dominance overshadowed U.S. center Alonzo Mourning's best game of the tournament. Mourning, of Georgetown University, finished with 26 points on 13-of-18 shooting. He also had a game-high 11 rebounds and used his quickness to embarrass Yugoslav big man Vlade Divac, on loan from the Los Angeles Lakers.

But despite Mourning's success in the middle, U.S. Coach Mike Krzyzewski had no answer for Petrovic. Nor, for that matter, did he have an answer for 6-foot-9 forward Toni Kukoc, who played today like the Magic Johnson of the Balkans.

Kukoc finished with 19 points, including two of four three-pointers, but it was his nine assists that were spectacular. They came on pretty no-look feeds, long bounce passes off the dribble that seemed to have eyes, and slashing penetration moves that left the U.S. defense flat-footed. Krzyzewski kept sending fresh players out to stop him. No one came close.

This same Yugoslavian team, minus Petrovic and Divac, defeated the United States in the final at last month's Goodwill Games in Seattle. Today's loss, said Krzyzewski, was no real surprise.

"I felt coming into the tournament that they were the best team," he said. "I thought our team played very well. If we hadn't played well today we would have lost by 30, because the other team played great."

"Great" about says it. The Yugoslavs were cool, professional, poised and talented. Even when the game was close, there was never really the sense that they were in danger.

One of the key factors was their success in holding U.S. guard Kenny Anderson to mortal numbers -- 12 points and seven assists -- and keeping him from taking over the game, as he did against Argentina, Spain and other hapless teams earlier this week.

The Yugoslav team smothered him. They tried to deny him the ball, and when he got it they kept him out of the middle.

Billy Owens, still suffering from a sore back, scored 12 points for the Americans.

Mourning established himself early, scoring six of the U.S. team's first eight points, all down low. When the bulkier Divac leaned on him there was little he could do, but once Mourning got free he was much quicker off the floor on his little turnaround jump-hooks.

But then Kukoc began to orchestrate, and the Yugoslavs went up by 11 points. Mourning picked up his third foul with 2:15 left in the first half -- a cheapie on Divac, who was about to score on a fast break -- and the Yugoslavs held an eight-point lead at halftime, 51-43.

In the second half, the Yugoslavian team opened up. The United States couldn't stay with Petrovic or Kukoc man-to-man. But whenever they went to a zone, the Yugoslavs managed to whip the ball around to the open man faster than the defense could adjust. If things broke down entirely, Kukoc drove the lane and made something happen.

The Americans pulled within three, but then forward Zarko Paspalj, a member of the San Antonio Spurs, hit a three-pointer, Petrovic hit another three-pointer after a U.S. miss, and suddenly the lead was back up to nine.

Paspalj made all three of his three-point shots as Yugoslavia connected on 11 of 19 overall. The United States made three of six three-pointers.

With about seven minutes left, the U.S. squad had what looked like a lapse in concentration. Their passes got sloppy, they stopped boxing out underneath, they took a few bad shots and suddenly the lead was 19 points. For all intents and purposes, the game was out of reach.

The United States made one last run to get the lead under 10, but it was too late. Mourning fouled out with 1:01 left, leaving to an ovation.

Yugoslavian Coach Dusan Ivkovic attributed the victory to the "mental state and preparation" of his squad. Krzyzewski attributed the loss to Petrovic, the 25-year-old guard who shot out the lights.

"I'm mad at the Portland Trail Blazers for letting him play," Krzyzewski said. "Whatever the highest level is in basketball, Petrovic was at that level today. I went up to him to congratulate him at the end. He was great. . . . On our team, Alonzo had that same kind of game."