Stan Wawrinka secured a quarter-final with nine-time champion Roger Federer after a 6-3 3-6 7-5 win over American Frances Tiafoe at the Swiss Indoors.
The 34-year-old seventh seed, who lost to Andy Murray in last week's European Open final, won on his fourth match point in two hours 32 minutes in Basel.
Three-time Grand Slam winner Wawrinka has won only three times in 26 previous meetings with fellow Swiss Federer.
Third seed Stefanos Tsitsipas beat Ricardas Berankis 6-7 (4-7) 6-2 6-4.
Greek Tsitsipas, 21, won in two hours one minute and plays either Filip Krajinovic or fifth seed Fabio Fognini in the last eight.