FRANKFURT -- Andre Agassi's remarkable year has continued with a victory over Michael Chang that puts him in the semifinals of the ATP Tour world tennis championship.


The U.S. Open champion defeated fellow American Chang 6-4, 6-4 for his second victory in the round-robin event as he clinched a place on Thursday in the top two of his red group.


The leading two from each group of four players qualify for the semifinals.


Agassi started the year in 24th position in the rankings and with his wrist in plaster.


But victory in the U.S. Open and a defeat of world number one Pete Sampras on his way to the prestigious Paris Open title earlier this month has brought him to the year-ending event second in the rankings.


The long-haired, 24-year-old from Las Vegas again showed the consistency which could bring him the prestigious title for the first time since 1990.


Agassi played some brilliant shots from the back of the court against Chang.


While Agassi's place in Saturday's semifinals was secure, the other group was wide open after Sampras beat Stefan Edberg 4-6, 6-3, 7-6 to keep alive his chances of progression.


Sampras, 23, showed why he is rated the best player in the world when he produced his best tennis under intense pressure.


He lost his opening match to Boris Becker on Wednesday and, seemed to be heading out of the tournament when he dropped the first set 6-4 against former Wimbledon champion Edberg.


But Sampras produced his best tennis in the crucial final set and clinched the victory by winning the third-set tiebreak 7-3.


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Proving Paris was no fluke, Mary Pierce ousted defending champion and top-seeded Steffi Graf on Thursday night to grab the first semifinal berth in the season-ending Virginia Slims Championships in New York.


Pierce, who ousted Graf from the French Open, beat her this time 6-4, 6-4 at Madison Square Garden.


Gabriela Sabatini, who ended Martina Navratilova's remarkable career Tuesday night, also won her quarterfinal match , against Julie Halard of France, 2-6, 6-2, 6-3.


Pierce, the No. 5 seed, moved into Saturday's semifinals against the winner of Friday's quarterfinal between No. 4 Jana Novotna and No. 7 Lindsay Davenport. Sabatini will take on either Wimbledon champion Conchita Martinez, who is seeded third, or No. 8 Kimiko Date of Japan.


Earlier, Navratilova made her final appearance in these championships. Two nights after she fell to Sabatini in singles, Navratilova and Manon Bollegraf of the Netherlands lost 6-2, 6-4 to Novotna and Arantxa Sanchez Vicario in a semifinal doubles match.


While she officially has retired from singles on the WTA Tour, Navratilova has hinted she might continue to play doubles.


"It is a possibility," she said. "I may want to come back to it more than I think because I'll want to do something that I do really well because in everything else I'll be a total beginner."


Neither Sabatini nor Halard was expected to be around in the quarterfinals. One day before Sabatini expunged Navratilova from the field, Halard upset Sanchez Vicario, the French Open and U.S. Open champion.


Halard seemed to be continuing her surprising run when she broke Sabatini to begin the match. She broke her again in the seventh game before holding through deuce to win the opening set.


Both were hitting with pace, precision and depth, but it was Halard who was in control, keeping Sabatini on the run, then slamming a winner from either side. When Sabatini used drop shots to bring the baseline-hugging Halard to the net, Halard would respond with scoops and chips.


Then, after the two fought evenly through the first four games of the second set, Sabatini hit a shot that was called good. Halard thought otherwise, and from then on Sabatini was in control. She raced through the second set 6-2, then took a 4-1 lead in the final set before closing out the victory.


Graf won the Australian Open in January and was favored to annex yet another major title at the French Open. Instead, she was a semifinal victim of Pierce, who went on to lose in the title match.


Navratilova's doubles match wasn't pretty. Twice she served in the final set. Both times she was broken, her once penetrating serve now being hammered back for winners.


On the final point of her final match, she received serve, and netted a backhand return. The crowd gave perhaps the greatest women's player in history a standing ovation. (Reuters, AP)