Courier Shows He’s Focused and Clicking : U.S. Open: He drills 10 aces and defeats Muster. Sabatini and Graf win.

Jim Courier wandered out of his strange wilderness and into contention at the U.S. Open on Tuesday, thumping foot-sore French Open champion Thomas Muster in straight sets on a day when upsets reigned.

There was no indifference by Courier this time, none of the haphazard stretches or moody moments that have marked his descent in the rankings.

This time, for the better part of two hours, he was the Courier of old, drilling 10 aces, drumming baseline winners and reaching the quarterfinals with a 6-3, 6-0, 7-6 (7-4) romp over the No. 3 Muster, a clay court specialist who ripped up his feet on these hot hardcourts.

Courier, No. 14, will find out just how far back he’s come when he plays his next match against No. 5 Michael Chang, a 6-2, 6-2, 4-6, 6-3 winner over Michael Tebbutt.

Reaching the women’s semifinals were top-seeded Steffi Graf and No. 9 Gabriela Sabatini. Graf beat Amy Frazier 6-2, 6-3, and Sabatini downed Mary Joe Fernandez 6-1, 6-3, two days after Fernandez ousted defending champion Arantxa Sanchez Vicario.

“I’ve really progressed from match to match,” said Graf, who played a three-setter in the opening round and won every other match in straight sets. “My back is holding up really well.”

Graf has dominated Sabatini of late, but remembered losing to her in the final at the Open in 1990 when Sabatini won her only Grand Slam title.

“Her game keeps you off a little bit so you don’t get the rhythm,” Graf said.

Muster never got his rhythm against Courier. Muster’s bleeding blisters were covered with a yard of tape, but for all it mattered he might as well have played barefoot the way little Byron Black of Zimbabwe used to do. Black, who’s grown up to all of 5-foot-9, pulled the first upset of the afternoon by sending 6-foot-4, 1994 runner-up Michael Stich packing, 6-4, 6-4, 3-6, 2-6, 6-3.

“I played a lot of barefoot,” Black said of his youth on the grass courts his father, once a player at Wimbledon, installed back home. “I have very high arches. I started getting a very bad heel, and then I had to play in shoes, although my dad didn’t like me tearing up his court too much.”

Black tore up Stich with a variety of two-fisted forehands and backhands, and the net-charging Stich accommodated him with 79 unforced errors.

“I know how he plays, and I just think I got off to a very bad start,” said Stich, the No. 8 seed. “He didn’t make any unforced errors. From the third set on, I was just in charge. I changed my style. I went for more. I had my chance in the fifth set, that break-point for 2-1, but I just gave it away. I played a poor game, made a double-fault and missed an easy volley.”

Courier and Muster waged a fierce baseline duel, slugging hard all the way, but Courier took more chances and put away far more winners--42 to 14--while out-acing Muster, 10-0.

“Personally, I feel good going out against Thomas on any surface, even clay,” Courier said. “He’s had a phenomenal year.”

Once the best player in the game, the winner of four Grand Slam titles from 1991 to 1993, Courier lost in the second round of the Open a year ago and drifted in this year on a whimper.