Unseeded Russian Yevgeny Kafelnikov produced one of the biggest shocks of the clay court season by knocking out third seed Carlos Moya 6-4 7-6 (7/4) to advance to the quarter-finals of the Telecom Italia Masters in Rome.
The other top-half seeds to fall were Roland Garros champion Albert Costa (seventh) and Tennis Masters Monte-Carlo finalist Guillermo Coria (15th).
Costa, who lost in the second round of Tennis Masters Monte-Carlo, was beaten 7-5 4-6 6-1 by fellow Spaniard Felix Mantilla.
Coria was beaten 6-4 6-3 by Croatian Ivan Ljubicic, who has not dropped a set in three matches this week.
Ljubicic is attempting to win through to his first Tennis Masters Series semi-final and next plays Mantilla.
Fourth seed Roger Federer improved to 8-0 on the clay court season with a ruthless 6-1 6-1 demolition of Spaniard Tommy Robredo.
Federer next meets Italian wild card Filippo Volandri, who defeated Czech Radek Stepanek 6-3 6-4.
Rainer Schuettler advanced to his first clay court Tennis Masters Series quarter-final with a 6-4 7-6 (7/2) win over Jiri Novak.
Schuettler, who also reached the quarter-finals in Munich last week, now meets second seed Juan Carlos Ferrero after the Spaniard came from behind to beat Gaston Gaudio 5-7 6-0 6-2 in the final singles match of the day.