Michael Chang won the last four games to upset top-ranked Stefan Edberg 6-4, 4-6, 7-5 on Tuesday in the opening round of the $6 million Grand Slam Cup, the richest tournament in tennis history.

Chang, who trailed 5-3 in the decisive set, broke Edberg's last two service games to win the error-filled match."I knew I had a decent chance against him, I've played him before and he's won some and I've won some," Chang said.

Pete Sampras and Goran Ivanisevic also advanced to the second round. Sampras, the U.S. Open champion who is seeded fourth, overcame a sloppy start to beat Andrei Cherkasov of the Soviet Union 5-7, 6-2, 7-5. Ivanisevic, the fifth seed from Yugoslavia, ousted Kevin Curren 7-6 (7-3), 7-6 (9-7).

In the other opening-day match, France's Henri Leconte beat Thomas Muster of Austria, 6-3, 6-4.

The 16-man field was determined on the basis of results in the four Grand Slam tournaments of the year - the Australian, French and U.S. Opens and Wimbledon. The winner gets $2 million and first-round losers receive $100,000.

Chang's stamina and determination prevailed over Edberg, who made too many unforced mistakes on his usually perfect volleys.

The victory leaves Chang trailing 5-3 in career clashes against Edberg. Chang beat Edberg when he became the youngest Grand Slam winner at the 1989 French Open.

Edberg was serving for the match at 5-4, but double-faulted and hit a volley wide to allow Chang pull even. Chang then held his serve at love, the first love game of the match, then got to match point on a double-fault before passing Edberg at the net for the victory.

"The year is finished at last, and that's one good thing," said Edberg, who won only three points in the last three games. "I missed a lot of easy shots, it's hard to get motivated after such a tough year."

Sampras served 16 aces but struggled with his second serve and his ground strokes.

"I rely on my first serve maybe too much," Sampras said.

He lost the first set when he committed two double faults. On the first, he fell behind 15-40. The 19-year-old American then served an ace but followed with another double fault to give Cherkasov the set.

Sampras quickly took control and dominated the second set, firing three aces on the last four points to win. He had a chance to put the match away after going up a break for a 5-4 lead in the final set, but hit a forehand long on the third break point.

But the Soviet was unable to take advantage. A spectacular passing shot down the line gave Sampras two break points and when Cherkasov netted a backhand, the American regained the lead.