Two-time champion Juan Martin del Potro and top-seeded Stan Wawrinka advanced to the Swiss Indoors quarter-finals on Thursday.
Del Potro beat fifth-seeded David Goffin of Belgium 7-5, 6-3, while Wawrinka had 16 aces as he beat American player Donald Young 7-6 (7-4) 6-7 (3-7) 6-4.
Both players held their serve in the first set and dropped it once in the second. Wawrinka, the US Open champion, took the only chance he got on Young's serve in the deciding set.
Del Potro, who won the Stockholm indoor title Sunday, extended his winning streak to seven matches - six against players higher in the standings than the 42nd-ranked Argentine player.
Goffin, who beat Del Potro at the Shanghai Masters two weeks ago, struggled with his second serves and was broken once in each set.
Del Potro won back-to-back titles at Basel in 2012 and 2013 but missed the last two editions due to left wrist injuries that dropped his ranking sharply.
The 28-year-old will play No. 5 Kei Nishikori of Japan on Friday.
Wawrinka, who was also taken to three sets in the first round, next faces Mischa Zverev of Germany, who beat Guido Pella of Argentina 6-4 6-2.
He broke Pella's serve three times and saved both chances on his own serve.
Earlier, fourth-seeded Marin Cilic - the 2014 US Open champion - had 10 aces in a 6-0 7-6 (7-4) win over Pablo Carreno Busta.
Cilic lost only five points in the first set against the 32nd-ranked Spaniard. The second set went with serve, and Cilic trailed in the tiebreaker before reeling off seven straight points.
Cilic next plays Marcel Granollers of Spain, who beat eighth-seeded Jack Sock of the United States 6-3 6-1.
Earlier, Gilles Muller of Luxembourg earned a spot in the last eight against Federico Delbonis of Argentina. Muller beat Florian Mayer of Germany 6-3 6-2.
