Top seed Andre Agassi and third seed Mardy Fish were upset by lower-ranked opponents in the quarter-finals of the Mercedes-Benz Cup in Los Angeles on Friday.
Agassi, who won the tournament in 1998, 2000 and 2001 and also claimed his 800th career victory earlier in the week, was upset by Germany's Tommy Haas 7-6, 6-7, 6-3 in the final match of the day.
Agassi had gone out to a 5-1 first set lead, which he blew as Haas, who missed all of last year while recovering from two shoulder operations, broke twice to force the first set tiebreak.
Haas could have won in straight sets after holding two match points in the second set tiebreak, but the 34-year-old Agassi won the final four points to force the decider.
Fish, who had struggled in earlier matches, was beaten by France's Cyril Saulnier 7-6, 7-6. The 28-year-old Frenchman had won their only other meeting, on carpet in Lyon last year.
Jeff Morrison, who had upset second seed Paradorn Srichaphan in the second round, made his first ATP tour semi-final this year with a 6-3, 6-4 victory over South Africa's Wesley Moodie. He is the only American to reach the last four.
Britain's Greg Rusedski, the Hall of Fame winner last week in Newport, had his winning streak snapped at seven with a 6-1, 6-4 defeat to Germany's Nicolas Kiefer.
Kiefer will meet Morrison while Haas will play Saulnier in the semi-finals.
