Croatia's Ivo Karlovic banged down 21 aces as he upset the 13th seed Gael Monfils of France 6-4 6-7 7-6 in the first round of the Cincinnati Tennis Masters.
Karlovic, who beat Roger Federer on his way to the semi-finals last year, won the deciding tiebreak 7-2 to advance to the second round after two hours and 10 minutes.
The former world number one Marat Safin eased past American Robby Ginepri, while seeds Gilles Simon of France and Croatia's Marin Cilic also won.
And Jose Acasuso of Argentina set up a second-round meeting with Federer by beating Lukasz Kubot of Poland but the 15th seed Tommy Robredo of Spain fell to Frenchman Jeremy Chardy.
And the world number six Juan Martin del Potro of Argentina, withdrew citing fatigue after his loss to Andy Murray in the Montreal Masters final.