Rafael Nadal suffered a shock quarter-final loss to Nick Kyrgios at the ATP Western and Southern Open, while Dominic Thiem was also upstaged by David Ferrer.
Back-to-back matches for top seed and incoming world number one Nadal appeared to catch up with him as he lost in straight sets to Kyrgios on Friday.
Austrian third seed Thiem crashed out of the ATP 1000 tournament following his upset defeat against veteran Ferrer in Cincinnati.
Grigor Dimitrov and John Isner also won through to the final four.
KYRGIOS STOPS NADAL
A semi-final berth was a step too far for Nadal, who went down 6-2 7-5 to his Australian opponent.
After rain wreaked havoc on Thursday, 15-time grand slam champion Nadal returned to beat Albert Ramos Vinolas in the last 16, while Kyrgios rallied against Ivo Karlovic.
Kyrgios looked the fresher of the two players as he dismantled Nadal in the opening set and kept his composure in the second.
"He obviously is a tough match always," said Nadal. "Nick is a great player, but I played poorly. I started the match well and then I played a very bad game in the second set when he broke me. I played some good points. He had some mistakes and I was able to be back in the match. And then I played a terrible game. So it was a bad match for me. Congrats to him. That's it."
FERRER FOILS THIEM
It has been a long time coming but Ferrer is back in the ATP 1000 semi-finals.
Ferrer prevailed 6-3 6-3 against Thiem for his first top-tier semi in two years.
A finalist in 2014, Ferrer will contest his first final-four match since Paris in 2015.
He will next face Kyrgios for a place in the decider.
DIMITROV TO PLAY ISNER
The Bulgarian seventh seed outclassed Yuichi Sugita 6-2 6-1.
Dimitrov broke the Japanese at the beginning of the first set and twice in the second to move within a win of his maiden 1000 final.
"It's a good feeling, for sure," said Dimitrov. "It's a good feeling. I like playing in Cincinnati. I love that centre court, as well. I think all that brings me good memories and just a positive way of thinking when I come out there on the court."
Isner – the 2013 runner-up – awaits in the semis after he saw off fellow American Jared Donaldson 7-6 (7-4) 7-5.
With 25 aces and 90 per cent of first serves won, Isner powered into the next round as he seeks his fourth appearance in an ATP 1000 final.