Top-seeded Stan Wawrinka let a second-set lead slip away, but he recovered to beat qualifier Donald Young of the United States 7-6 (4), 6-7 (3), 6-4 on Thursday to advance to the quarterfinals at the Swiss Indoor Basel.
Wawrinka served at 5-3 in the second set, but could not close it out against the 83rd-ranked Young, who won the tiebreaker.
Wawrinka settled down to win the third set, saving the only break point against him while serving six aces in the final set. Wawrinka will next face 72nd-ranked Mischa Zverev of Germany, who eliminated Guido Pella of Argentina 6-4, 6-2 in his second-round match.
Unseeded Juan Martin del Potro of Argentina continued his 2016 resurgence by beating fifth-seeded David Goffin of Belgium 7-5, 6-3.
Del Potro, who won last week's Stockholm Open, never lost his serve, saving all four break points against him.
"I played well in the big moments. I broke his serve once in each set, and that was enough to win today," said del Potro, who will next face Kei Nishikori.
Del Potro is 4-0 against Nishikori and has never lost a set to the Japanese star.
"(Kei) is so fast and so aggressive with his backhand. My game has changed since my (wrist) injury but if I serve well, I have a chance to win."
Fourth-seeded Marin Cilic of Croatia nearly lost the second set of his match, getting behind 4-0 in the tiebreaker, but he rallied to win the final seven points in his 6-0, 7-6 (4) victory over Pablo Carreno Busta.
Cilic's next opponent is Marcel Granollers of Spain, who defeated eighth-seeded Jack Sock of the United States 6-3, 6-1.
"I came out quite fast in the first set but I expected Pablo to find his rhythm," Cilic said. "Everything was going in my favor in the first set. I wasn't playing worse in the second, I just missed some opportunities and that gave him extra time to settle down. It was quite tight in the tie-break. It was a mental battle. I knew it was critical to finish the match in two sets and I was lucky to pull it out."