Defending Geneva Open champion Stan Wawrinka was given an easy passage into this year's quarter-finals after second-round opponent Rogerio Dutra Silva retired hurt.

The Swiss top seed was leading 5-2 in the first set when an ankle injury put paid to his Brazilian opponent's chances.

Wawrinka will now face Sam Querrey in the last eight following a 6-2 6-3 win for the American over qualifier Franko Skugor of Croatia.

Lucky loser Cedrik Marcel-Stebe marched on after an injury halted Janko Tipsarevic's campaign, with Andrey Kuznetsov waiting in the next round after his surprise 7-5 6-1 win over third seed Albert Ramos Vinolas.

Fourth seed John Isner also fell in the second round, losing 6-4 6-7 (5-7) 6-3 to Germany's Mischa Zverev, while Steve Johnson got the better of Horacio Zeballos in a 6-1 6-3 victory.