Cincinnati: Ivo Karlovic banged down 21 aces as he upset 13th seed Gael Monfils 6-4, 6-7, 7-6 in the first round of the Cincinnati Masters.
The 6-feet-10 (2.08 metres) Croat, 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, 10 minutes.
After taking the first set thanks to one break, Karlovic led 5-4 in the second-set tiebreak, with two serves to come, but Monfils reeled off three superb points in a row to force a decider.
The Frenchman saved three break points in the fourth game of the third set but Karlovic played a superior tiebreak to move through to a clash with another Frenchman, Paul-Henri Mathieu, a 6-7, 7-5, 6-3 winner over German Mischa Zverev.
Ninth seed Gilles Simon eased into the second round with a 6-3, 6-2 win over American wildcard Wayne Odesnik. He will now play Russian Igor Andreev, who beat Nicolas Kiefer of Germany 6-1, 7-5.
Croatia`s 14th seed Marin Cilic beat former world number one Juan Carlos Ferrero 6-3, 6-4. He will play David Ferrer of Spain in the second round after he beat Stanislas Wawrinka of Switzerland 7-5, 6-2.
Jose Acasuso of Argentina set up a second-round meeting with world number one Federer by beating Lukasz Kubot of Poland 6-4, 6-3.
Ivan Ljubicic, Benjamin Becker and Nicolas Almagro also advanced in the day`s early action.
World number six Juan Martin del Potro withdrew from the tournament, citing fatigue, organisers said.
The Argentine was beaten by Andy Murray in the final of the Montreal Masters on Sunday, having also won a tournament in Washington the previous week.
Del Potro is replaced in the draw by lucky loser Julien Benneteau of France.
Later on Monday, former world number one Marat Safin, who is to retire at the end of the year, faced American Robby Ginepri.