Ukraine's Sergiy Stakhovsky sprang a first round surprise at the Quatar Tennis Open by knocking out fourth seed Mikhail Youzhny 7-6 6-2.
Stakhovsky, ranked 60th in the world, smashed nine aces as he avenged his 2009 Kremlin Cup final defeat by the Russian.
The world number 19 Youzhny served five double faults as he slumped to defeat.
The fifth-seeded Serb Viktor Troicki hit 10 aces in a 6-1 7-5 win over Daniel Gimeno of Spain that took just 56 minutes.
Spaniard Albert Montanes, seeded sixth, lost 6-2 7-5 to Latvian Ernest Gulbis while seventh seed Ivo Karlovic of Croatia beat Italian Fabio Fognini 6-4 6-4.
World number one Roger Federer begins his campaign against Belgian Christophe Rochus and second-ranked Rafael Nadal takes on Italian Simone Bolelli.