Zagreb - German qualifier Bjorn Phau has upset second-seeded Mikhail Youzhny to reach the quarter-finals of the Zagreb Indoors on Thursday.
Phau beat the Russian 4-6, 7-5, 6-1 and will compete in his first quarter-final since Stuttgart in 2012.
Another qualifier and a lucky loser also made the last eight.
Youzhny, the 2012 champion, was playing well until he lost his serve in the second set when he foot-faulted.
Phau used the opportunity to win four games in a row and turn the match around.
"It was not the foot fault that caused me to lose the match," Youzhny said, adding he felt sick during play.
Third-seeded Philipp Kohlschreiber of Germany defeated Andrey Golubev of Kazakhstan 6-4, 6-2, and Ivan Dodig notched his fourth straight win against Croatian countryman Ivo Karlovic 7-6 (5), 6-3.
Russian qualifier Andrey Kuznetsov beat eighth-seeded Igor Sijsling of Netherlands 6-1, 3-6, 7-6 (5), and lucky loser Daniel Evans of Britain beat Michael Berrer of Germany 1-6, 6-1, 7-6 (4).
Dudi Sela of Israel also advanced, defeating Lukas Lacko of Slovakia 6-3, 6-2.
Results from fourth day of the ATP Zagreb Indoor Open on Thursday (x denotes seeding):
Andrey Kuznetsov (RUS) bt Igor Sijsling (NED x8) 1-6, 6-3, 7-6 (7/5)
Philipp Kohlschreiber (GER x3) bt Andrey Golubev (KAZ) 6-4, 6-2
Ivan Dodig (CRO x4) bt Ivo Karlovic (CRO) 7-6 (7/5), 6-3
Daniel Evans (GBR) bt Michael Berrer (GER) 1-6, 6-1, 7-6 (7/4)
Dudi Sela (ISR) bt Luks Lacko (SVK) 6-3, 6-2
Bjrn Phau (GER) bt Mikhail Youzhny (RUS x2) 4-6, 7-5, 6-1