Dominic Thiem and Grigor Dimitrov beat the rain to progress at the Western and Southern Open as bad weather eventually washed out play in Cincinnati.
Conditions early on Thursday allowed players to take to the court and third seed Thiem overcame in-form Adrian Mannarino to reach the quarter-finals of the ATP 1000 event.
Dimitrov - the seventh seed - got the better of Juan Martin del Potro in windy and humid weather.
Conditions deteriorated later in the day as top seed and incoming world number one Rafael Nadal failed to take to the court, with tournament officials eventually cancelling play approaching midnight in Cincinnati.
Australian Nick Kyrgios was trailing Ivo Karlovic 4-3 in the opening set when the rain set in, with the winner of that match set to face either Nadal or Albert Ramos-Vinolas on Friday.
It was always going to be a tough match against Frenchman Mannarino, who advanced to the quarter-finals at the Rogers Cup last week.
He forced Thiem to two tie-breaks as the Austrian prevailed 7-6 (7-4) 7-6 (7-3).
Next up for Thiem after his two-hour battle is Spanish veteran David Ferrer, who defeated compatriot Pablo Carreno Busta 6-4 6-4.
DIMITROV FINALLY BEATS DEL POTRO
For the first time in six matches, Dimitrov claimed a win over Del Potro.
Dimitrov won through to the last eight at an ATP 1000 event for the eighth time thanks to a 6-3 7-5 victory.
"He's a tricky opponent... a super-experienced player," said Dimitrov. "I definitely had to stay away a little bit from that forehand. I knew if I keep the ball low on his backhand side and just kind of work my way into the court, it would have been the right thing to do. I think I did this thing very, very well today. The short slice really made him very uncomfortable, and he was giving me a lot of short balls, so I could start moving him with my forehand. It was also a bit of a mind game, because we know our game pretty well."
Standing in the way of Dimitrov and consecutive Cincinnati semi-finals is Japan's Yuichi Sugita, who rallied to defeat Karen Khachanov 6-7 (0-7) 6-3 6-3.
ISNER OVERCOMES TIAFOE AND RAIN
John Isner booked his spot in the quarters with a 7-6 (7-4) 7-5 victory against fellow American Frances Tiafoe.
Tiafoe stunned Alexander Zverev to reach the last 16 but he was unable to back it up against 2013 runner-up Isner, who fired down 27 aces.
It is another all-American clash on Friday as Isner faces Jared Donaldson after his 6-4 7-6 (7-4) win against Nikoloz Basilashvili.