Third seed Viktor Troicki was ousted by world No. 112 Malek Jaziri in their second-round match at the Kremlin Cup in Moscow on Wednesday.
Troicki, who won the tournament in 2010 but lost the following final to Janko Tipsarevic, looked to have played his way out of trouble after dropping the first set. But the Tunisian surged back for a 6-1, 3-6, 6-2 win and a place in the quarterfinals.
There the 28 year old faces Lukas Rosol of the Czech Republic, who had earlier sent another seed tumbling in Denis Istomin.
Elsewhere, Flavio Cipolla of Italy completed a straight-sets win over Russian wild card Teymuraz Gabashvili 6-4, 6-4.
Earlier, Ivo Karlovic defeated Simone Bolelli of Italy 6-4, 7-6(4), while tournament newcomer Jerzy Janowicz beat world No. 80 Benjamin Becker of Germany 7-6(6), 6-3.
The Polish 22-year-old will play seventh seed Carlos Berlocq of Argentina in the second round.
At the start of play, Japanese eighth seed Ito Tatsuma dispatched qualifier Konstantin Kravchuk of Russia 7-6(7), 2-6, 6-3.
