(CNN) -- Top seed Roger Federer eased into the second round of his hometown event in Basel after Ukrainian opponent Aleksandr Dolgopolov retired through injury.
Federer was poised for victory, leading 6-4 5-2 in the Swiss Indoor tournament, when his 48th-ranked opponent was forced to quit with an ankle problem after a tumble on court.
The Swiss, who chalked up nine aces and three breaks of serve, will face either Serb Janko Tipsarevic or Denis Istromin of Uzbekistan.
Federer is looking for his fourth Basel title in five years, after last year's final defeat by Novak Djokovic ended his run of three successive victories.
Meanwhile, in the Valencia Open in Spain, third seed Fernando Verdasco had no problems reaching the second round with a straight sets victory over American Michael Russell.
Verdasco went through 6-4 6-1 and joins Frenchman Gilles Simon and Swiss Stanislas Wawrinka -- who also both won in straight sets -- in the next round.
However, France's Jo-Wilfried Tsonga, the world number 13, confirmed on Monday he had withdrawn from the tournament because of a recurring knee injury.