Second seed Tomas Berdych double-faulted on match point to hand Feliciano Lopez victory in their quarter-final at Queen's Club.
Lopez, seeded 10th, saw off the Czech 6-4 7-6 (9-7) to reach the last four at the Aegon Championships.
The Spaniard goes on to face another Czech, Radek Stepanek, who beat Kevin Anderson 1-6 6-3 6-2.
Top seed and Australian Open champion Stanislas Wawrinka beat Australian Marinko Matosevic 7-5 6-3.
The Swiss will next play fourth seed Grigor Dimitrov, who had a walkover after eighth seed Alexandr Dolgopolov pulled out with a thigh strain.
Wawrinka, 29, had to work hard in the opening set against an in-form Matosevic, but the Swiss gradually found his range.
After failing to convert from 0-40 in game eight, Wawrinka made the breakthrough to clinch the set in game 12 and took a grip on the match with a run of five games in a row.
"So far I'm playing good," he said. "I'm really happy with that match. I'm serving well, very aggressive, and I'm feeling really happy on the grass."
Lopez, 32, again showed his pedigree on grass by seeing off Berdych, the world number six, in a tight match.
He grabbed what proved to be the only service break of the match in the first set, and came back from 6-3 down in the second set tie-break.
Having looked on course to force a third set, Berdych cracked under the pressure and sent down a double-fault when facing match point.
"I got the early break in the first set even though the match was very, very close," said Lopez. "But my serve was working perfectly today."
Stepanek had earlier followed up Thursday's win over Andy Murray with another impressive performance, fighting back to beat seventh seed Anderson.
"Experience definitely helps," said the 35-year-old, through to his first ATP semi-final for over two years.
"Always when you start to play the grass-court season, you're looking to play as many matches as you can to get comfortable, to be friends with the grass.
"That's what I'm doing here."
Britain's Jamie Murray and Australian John Peers came through a dramatic tie-break to beat Anderson and Israel's Jonathan Erlich 6-4 7-6 (16-14) and reach the semi-finals.
Meanwhile, Switzerland's Roger Federer had a walkover in the quarter-finals of the Gerry Weber Open in Halle after Lu Yen-hsun pulled out because of back problems.
Second seed Federer, who is looking to win the event for a seventh time, will play fourth seed Kei Nishikori in the last four.
Top seed Ana Ivanovic eased into the semi-finals of the Aegon Classic in Birmingham with a 6-1 6-4 victory over Klara Koukalova.