Rome - Unseeded American John Isner battled into the Rome Masters semis on Friday with a 7-6 (7/3), 2-6, 7-6 (7/2) win over Croatian sixth seed Marin Cilic.
Isner, ranked 24th in the world, reached the last eight on Thursday when he upset world No 3 Stan Wawrinka of Switzerland 7-6 (7/1), 6-4.
The towering American will now meet the winner of the quarter-final between 20-year-old German Alexander Zverev, seeded 17th, and big-serving Canadian Milos Raonic.
Later Friday, seven-time champion Rafael Nadal, seeded fourth, meets Austrian eighth seed Dominic Thiem in a repeat of last week's Madrid Masters final, won by the Spanish clay court king.
In the other quarter-final unseeded Argentinian Juan del Potro faces former four-time champion and second seed Novak Djokovic of Serbia.
Results on the sixth day of the Rome Masters on Thursday (x denotes seeding):