Pete Sampras has crashed out of the second round of the Cincinnati Masters Series after losing 6-4 6-4 to Alberto Martin.
Martin broke Sampras' serve in the fifth game of both sets to win, and leave the American stuck without a title for 16 tournaments - his longest drought since 1990.
Sampras won the first game with three consecutive aces, but had only three more the rest of the match. He double-faulted nine times.
"I didn't serve well. I didn't really do much of anything," Sampras said. "It really was a disappointing performance - not acceptable."
In other matches Top-seeded Gustavo Kuerten was forced into two tiebreakers in beating Tommy Haas 7-6 7-6.
Fifth-seeded Lleyton Hewitt also struggled, needing three sets to beat Bohdan Ulihrach 6-2 5-7 6-2.
Elsewhere, sixth-seeded Yevgeny Kafelnikov beat Fabrice Santoro 6-1 6-4 and eighth-seeded Patrick Rafter beat Xavier Malisse 6-0, 6-3.
Wimbledon champion Goran Ivanisevic beat Nicolas Escude 6-3 6-4 to advance to Thursday's match with Kuerten.
Four seeded players, including Sampras, were knocked out on Wednesday.
Hicham Arazi beat fourth-seeded Juan Carlos Ferrero 6-7 6-4 6-4, James Blake beat tenth seed Arnaud Clement 7-5 6-4 and Ivan Ljubicic knocked out 13th seed Carlos Moya 7-6 7-5.