Argentine Juan Martin del Potro has overcome a second-set lull to defeat Portugal's Joao Sousa in the opening round of the Swiss Indoors.
The fourth seed broke serve five times to complete a 6-1 4-6 6-1 victory defeat.
He will face Julien Benneteau in the next round after the French veteran beat American Donald Young 6-4 6-2.
"I need to play better for sure if I want to stay here longer," Del Potro said.
"But after all of my wrist problems, this is good for me.
"I have a tough match against Benneteau.
"But I really want to play Federer again in his hometown, that is always a great moment for me."
Del Potro has handed the Swiss icon his only two losses at the St Jakobshalle since 2010, winning finals in 2012 and 2013. The duo will face each other in the final if they progress through the draw.
Del Potro remains on target for a possible spot in next month's eight-man ATP Finals in London if he keeps up his sizzling form.
In other first-round matches, seventh-seeded Adrian Mannarino beat Ruben Bemelmans 7-6 (7-0) 4-6 6-1 while Croatian Borna Coric edged Swiss Henri Laaksonen 6-7 (8-10) 6-1 6-3 and Hungarian Marton Fucsovics thrashed Jared Donaldson 6-0 6-1.
In second round action, Belgian third seed David Goffin cruised past Hyeon Chung 6-4 6-1 to set up a quarter-final showdown with American fifth seed Jack Sock, after his 6-4 2-6 6-4 victory over Dutchman Robin Hasse.
Sixth-seeded Spaniard Roberto Bautista Agut defeated American Ryan Harrison 6-3 7-6 (7-1) to reach the last eight.
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