Struggling at times to find her rhythm and concentration, and pushed hard by the unseeded Austrian, Judith Wiesner, the defending champion called on her vast experience to fashion a 7-5, 6-3 quarter-final win. "I guess for some reason it's a little difficult at present to focus very well on court," Graf said on the eve of her father's tax evasion trial, in which the joint world No 1 herself may be called upon to testify.
"I don't really have the most positive attitude out there," she admitted. "I'll definitely have to work on that."
Graf knows she will have to play a lot better if she is to claim her fifth US Open title in New York on Sunday. "Knowing I have so much experience of being in semis and finals of Grand Slams, I think definitely will help me a lot," she said.
The German now meets the 15-year-old Swiss girl, Martina Hingis, who beat the Czech seventh seed, Jana Novotna 7-6, 6-4.
"Maybe I haven't played the best tennis in the last few rounds," Graf said. "But I know when it gets down to the important matches I'm usually up there, so hopefully it will be the same again."
Monica Seles took just 48 minutes to crush Amanda Coetzer, 6-0, 6- 3. Seles now faces Spain's Conchita Martinez, the No 4 seed and the player she defeated in last year's semi-finals.
"I don't think she's unbeatable at all," Martinez, who has lost all eight of her matches against Seles, said optimistically. Martinez fought off three set-points in a first-set tie-break, then cruised to a 7-6 6-0 victory over America's Linda Wild.
Second seed Michael Chang, the little man with the big racket, made life difficult for himself before taking the first semi-final place in the men's competition with a 7-5, 6-3, 6-7, 6-3 win over the Spaniard, Javier Sanchez.
Apparently on his way to a straight-sets stroll after racing through the second set and going up two breaks in the third, Chang ended up in a four-set battle with the lowest ranked player left in the tournament, at No 67.
Sanchez, who had lost in the first round of eight of his previous nine Grand Slams, started playing inspired tennis. The older brother of the beaten women's third seed, Arantxa Sanchez Vicario, took Chang to a tie- break and dominated it, 7-2, to send the match into fourth set before the American reasserted his control of the proceedings.
Tim Henman's run of success in the United States Open was brought to an end at Flushing Meadow as Stefan Edberg took their fourth-round match in four sets to earn a quarter-final against Goran Ivanisevic, the No 4 seed.
Edberg beat Henman 6-7, 7-6, 6-4, 6-4 in a three-hour match. Despite the defeat, the British player will have acquired many admirers in the match with a sustained level of top-class play, mainly from the baseline.
A philosophical Henman added: "I still think I can reflect on a very good tournament, another positive step in my career. Stefan's obviously at the end of his and hopefully I'm at the beginning of mine."
In another fourth-round match, Pete Sampras, the holder, took the sting out of Mark Philippoussis's serve, blocking back anything he could reach, to knock out the Australian.
Sampras lost the duel of aces 17-11 but won the match 6-3, 6-3, 6-4 with a masterful performance in every other phase of the game. "When you're going against a 134mph serve, you'd better have your game face on," Sampras said. "His service is so hard, you almost have to guess. You hope you get that one break-point."