BUENOS AIRES, AUG. 14 -- The United States overcame a 13-point deficit with seven minutes to play, injuries to two star players and a career performance by a fellow American college player today to beat Australia, 79-78, then later clinched a semifinal berth in the World Basketball Championships.

The U.S. team advanced to Friday's semifinals when Puerto Rico beat Argentina, 92-76. The United States and Puerto Rico, the only undefeated teams in the tournament, meet Wednesday, with the top seed at stake.

The semifinal berth was shaky for a long time today, as Australia (0-2) nearly registered its first victory over the United States behind 7-foot-2 center Luc Longley, who plays at New Mexico.

Australia took a 70-57 lead with 7:17 to play after a three-pointer by Phil Smyth. The United States was playing without Billy Owens, who pulled a muscle in his back in the opening minute, and Kenny Anderson, who took an elbow in the face during a scramble for a rebound with 11:40 to play.

Yet the loss of Owens and Anderson did not seem to matter when the Americans swarmed on defense, led by reserves Lee Mayberry and Todd Day, teammates at Arkansas, and Alonzo Mourning of Georgetown.

Christian Laettner hit two free throws to start the U.S. team's 22-8 run to victory. After a free throw by Australia's Ray Borner, Day hit a three-pointer, his first points of the game and the first of 10 he scored in the final 6:31.

"We knew Billy wasn't going to play and we saw Kenny, and we sat on the bench and said someone had to step forward, and instead the whole bench stepped forward," Day said.

Australia scored three points on free throws to make it 74-62, then Mourning called the team together.

"They were on the foul line and we were down 11, and I called everyone together and said we were going to win the game," said Mourning, who finished with 8 points, 14 rebounds and 5 blocked shots. "Lee, Todd, Henry {Williams} and Doug {Smith} all stepped up to play some sensational defense and give us a big lift."

Day and Mourning each hit two free throws, and Smith and Day each scored on drives as Australia began to turn the ball over against the pressure defense. The U.S. squad trailed by 74-70 with 3:23 left.

Andrew Gaze (23 points) hit two free throws to restore the margin to six. But Smith converted a miss by Day, and Mourning stole the ball at midcourt and went in for a layup to get the United States within two points with 2:29 left.

Gaze, a former Seton Hall star, scored Australia's final points on two free throws 26 seconds later.

Turnovers led to a dunk by Day, a free throw by Day, and then the clincher -- Mayberry's steal of an inbounds pass and a layup after Day's free throw. With 1:17 to play, the United States had the lead -- its first since the first half.

Mourning blocked a shot by Longley on the next Australian possession and Day stuffed Gaze when he grabbed the rebound. The United States then opted for possession rather than attempt free throws after three Australian fouls, and time expired.

Australian Coach Adrian Hurley said: "We just gave the game away. We're sitting here analyzing why the U.S.A. played so badly. There were two teams out there; one kept its composure at the end."

The United States played poorly much of the game, shooting 10 for 28 in the first half, as Longley dominated inside. Longley, who had totaled 16 points and 15 rebounds in Australia's first four games, finished with 15 points, 13 rebounds and 6 blocked shots.

In an earlier game, Yugoslavia routed the Soviet Union, 100-77.