Roger Federer survived an opening-match fright by outlasting Canada's Vasek Pospisil 7-6, 5-7, 6-2 to claim his 300th Masters Series win and reach the third round of the Western and Southern Open in Cincinnati.
Back in action after losing to Jo-Wilfried Tsonga in the final of the Rogers Cup in Toronto on Sunday, third-ranked Federer appeared sluggish at times as he struggled to tame the 46th-ranked Canadian.
With the victory, the second seeded Swiss, a five-time champion on the Cincinnati hard courts, becomes the first player to reach 300 wins in the ATP Tour's elite Masters 1000 events.
Earlier, after a first-round bye, eighth-seeded Briton Andy Murray got his tournament off to a convincing start by easing past Portugal's Joao Sousa 6-3, 6-3.
But Taiwan's Lu Yen-Hsun shocked fourth-seeded Czech Tomas Berdych 3-6, 6-3, 6-4 while Poland's Jerzy Janowicz knocked off Bulgarian seventh-seed Grigor Dimitrov 6-4, 3-6, 6-3.
In evening matches, Frenchman Gael Monfils sent 13th seed Roberto Bautista Agut home with a dominant 6-4, 6-1 win in just under an hour.