Roger Federer won his 17th consecutive match at the Swiss Indoors on Thursday by dispatching Jan-Lennard Struff 6-3, 7-5 to reach the quarter-finals.
The top seeded Swiss is an eight-time winner of his home event and will next play against either Frenchman Gilles Simon or Latvia’s Ernests Gulbis.
Federer, 37, trailed to an early break but soon recovered for 3-all in the opening set before he broke for 5-3 to close out the opener in 27 minutes.
The second set stayed on serve until a fifth double-fault from Struff, which opened the door for Federer to move 6-5 ahead.
Moments later, the 20-time Grand Slam champion served out a 41st victory of the season with a volley into the empty court on his first match point to maintain his unbeaten run in Basel since 2013.
Fourth seed Stefanos Tsitsipas dominated Peter Gojowczyk 6-3, 6-1 to line up a quarter-final with one of his toughest NextGen rivals.
The Greek will face Russian Daniil Medvedev, who defeated Italy’s Andreas Seppi 7-6 (7/5), 6-2 in their second-round encounter.
Second seed Alexander Zverev ended the run of 174th-ranked Australian teenage qualifier Alexei Popyrin with a 6-4, 6-4 win.
The German next plays Spanish eighth seed Roberto Bautista Agut who continued his quiet progress through the draw, beating Serb Dusan Lajovic 6-7 (6/8), 6-3, 6-3.