World number one Roger Federer began the defence of his Cincinnati Masters with a 7-5 6-4 win over Paradorn Srichaphan of Thailand.
Federer won the 40th title of his career in Toronto
The Swiss now plays British number one Andy Murray, who beat Tim Henman in their first-round encounter.
World number two Rafael Nadal suffered a first-round scare before beating American wildcard Sam Querrey.
Nadal eventually triumphed 6-7 (5-7) 6-2 6-3 against the teenager, who is ranked 178th in the world.
In a battle of big serves, ninth-seeded Andy Roddick beat Daniele Bracciali of Italy 6-7 (6) 7-6 (4) 7-6 (5).
America's Roddick served 22 aces and Bracciali had 19 in a match that lasted two hours and 34 minutes.
Frenchman Gael Monfils also advanced after a 6-4 7-5 victory over Russian Marat Safin.
German 14th seed Tommy Haas defeated Spain's Fernando Verdasco 6-3 6-4, while Max Mirnyi of Belarus put out Xavier Malisse, who reached last week's Toronto quarter-finals, 7-5 4-6 6-3.