Roger Federer will meet Jo-Wilfried Tsonga next after beginning his grass-court season with a 7-6 (7-1) 6-3 win over Australia's John Millman in Halle.
Federer, 37, lost to Millman at last year's US Open and was given a thorough work-out by the world number 57.
Neither offered up any break points in the first set and, after Federer had swept the tie-break, the Swiss secured the only break of the second set.
Tsonga beat Federer in an epic five-set comeback at Wimbledon in 2011.
The French world number 77, who overcame compatriot Benoit Paire 6-4 7-5 in his own first-round match, also beat Federer in the pair's two most recent matches.