Roger Federer defeated Guido Pella 6-4, 6-4 to advance to the Stuttgart Open semifinals on Friday.
Despite the 75th-ranked Argentine producing one of his best matches on grass, Federer was hardly troubled.
With Federer serving for the match, Pella forced two break points for some late drama. But Federer answered with four points in a row to set up a meeting with the fourth-seeded Nick Kyrgios or Feliciano Lopez.
The Swiss great can reclaim the No. 1 ranking from Rafael Nadal with a win.
Defending champion Lucas Pouille faced Milos Raonic in the other semifinal.
Earlier Friday, Pouille defeated Denis Istomin of Uzbekistan 6-4, 6-7 (5), 6-3, and Raonic upset the third-seeded Tomas Berdych 7-6 (2), 7-6 (1).
(With AP Inputs)