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.
In his first meeting with world number 48 Tiafoe, who beat British number one Dan Evans in the previous round, Wawrinka served 14 aces and claimed the decisive break to win the match after a marathon 12th game containing six deuces.
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