Czech veteran Radek Stepanek claimed another impressive scalp at Queen's Club as he followed his shock win over Andy Murray by defeating South Africa's Kevin Anderson 1-6, 6-3, 6-2 in the quarter-finals on Friday.
Stepanek, ranked 42nd, ended defending champion Murray's 19-match winning run on grass in the previous round.
And the 35-year-old continued his giant-killing streak by fighting back from a set down to eliminate world number 18 Anderson to reach the last four at the Wimbledon warm-up for the first time in nine years.
Stepanek will play Feliciano Lopez on Saturday for a place in Sunday's final after the Spanish 10th seed enjoyed a surprise 6-4, 7-6 (9/7) success against world number six Tomas Berdych.
Stepanek seemed to be suffering a hangover from his stunning victory against Wimbledon champion Murray during a lethargic first set display that saw the big-serving 6ft 8in Anderson overpower his opponent with ease.
But Stepanek, supported again by compatriot and Chelsea goalkeeper Petr Cech, wrestled the momentum back to seal his latest impressive win after surviving a 15-ace barrage from the seventh seed.
"It's great to beat a top guy, but it's even tougher to back it up with a win again," said 15th seed Stepanek, who is bidding to win his first singles' title since 2011 in Washington.
"In the first set Kevin played perfect tennis. For a half hour I really had no chance.
"But I once won a match where I faced 78 aces. That was against Ivo Karlovic in the Davis Cup in 2009, so I knew I just had to wait and take my first chance."
Czech second seed Berdych, a former Wimbledon runner-up, was well below his best against Lopez, the smooth-moving left-hander who had beaten four-time Queen's champion Lleyton Hewitt in the second round.
- Aggressive -
Lopez, the world number 29, broke in the fifth game for a 3-2 lead and easily closed out the set.
The 32-year-old kept the pressure on in the second set and when Berdych double-faulted on match point, Lopez was able to celebrate his 50th win on grass and his first ATP Tour semi-final berth since Gstaad nearly a year ago.
"It was very close but I don't think I gave more than two break points in the whole match," Lopez said.
"I'm very happy with my performance. The way I play, on grass I have to be aggressive and today my serve was working perfectly."
All the upsets at this year's tournament mean there will be a first-time champion as the four previous winners in the draw -- Murray, Hewitt, Sam Querrey and Marin Cilic -- were knocked out before the quarter-finals.
Bulgarian fourth seed Grigor Dimitrov didn't have to break sweat to reach the semi-finals as his scheduled opponent, Ukrainian eighth seed Alexandr Dolgopolov, was forced to withdraw ahead of their match with a thigh strain.
Dimitrov will face top-seeded Swiss Stan Wawrinka after he defeated Australia's Marinko Matosevic 7-5, 6-3.
Matosevic, the world number 60, had earned headlines on and off the court this week after criticising Murray's decision to hire Frenchwoman Amelie Mauresmo as his coach and then defeating Cilic and Jo-Wilfried Tsonga en route to the last eight.
But he couldn't steal the limelight against world number three Wawrinka, who won his maiden Grand Slam in Australia earlier this year and is gradually getting back on track after losing three of his four matches before Queen's, including a first round exit at the French Open.
Wawrinka's win is an ominous sign for his remaining rivals as on each occasion he has made the last eight this year he has gone on to take the Chennai, Australian Open and Monte Carlo titles.