Gianluca Mager upset Dominic Thiem and then moved within reach of a maiden ATP Tour final as rain continued to impact the Rio Open.

Down a set when forced off on Friday, top seed Thiem failed to stave off a quarter-final loss once play resumed on Saturday.

Italian qualifier Mager turned his overnight advantage into a 7-6 (7-4) 7-5 victory before again taking to the court later in the day for his semi-final.

The 25-year-old's opponent, lucky loser Attila Balazs, earlier beat Pedro Martinez 2-6 6-4 6-2 but was left clinging onto a place in the tournament when the rain returned, the Hungarian trailing 7-6 (7-4) 3-3 against Mager.

The winner will likely face Cristian Garin in the final after the Chilean third seed opened up a 6-4 4-4 lead over Borna Coric in the other postponed semi-final.

Poor conditions also interrupted the Delray Beach Open, where Milos Raonic was unable to get underway against Reilly Opelka.

The big servers had their semi-final rescheduled for Sunday and will compete for a spot in the decider against Yoshihito Nishioka, who battled from a set down to defeat Ugo Humbert 1-6 6-4 6-0.

Nishioka has reached the final despite dropping the opener in three of his four matches at the ATP 250 event.

"After the first set I just figured out how to play against him and just kept trying to do it and then it worked," he said, as quoted by the ATP Tour.

"If I lose the first set it's okay, I just figure out how he's going to play, how I have to play against him and then from the second set I say, 'Okay, let's do it this way.'"