Unseeded Joao Sousa shocked top seed David Ferrer 6-2 7-6 (8/6) to reach the semi-finals of the Malaysian Open.
The Portuguese No 1 left the 31-year-old French Open runner-up reeling as he clinched his first ever victory over a top 10 player.
Sousa, 24, converted all three of his break point chances and denied Ferrer three of the four he earned.
He missed a match point opportunity when he served for victory at 5-4 in the second set, before rallying from a 4-6 deficit in the tiebreaker.
"I've never beaten a top 10 player before, let alone someone in the top five. This without doubt is my biggest victory," said world No 77 Sousa.
He will now meet fourth-seeded Jurgen Melzer in the final four in Kuala Lumpur after the Austrian swept past Federico Delbonis from Argentina, 6-3 6-2.
Afterwards, Melzer, 32, paid tribute to his younger brother Gerald, who gave him tips on an opponent he was meeting for the first time.
"Sure I called him and asked for his advice since he beat Delbonis before. I asked him for advice and whatever he said was true!
"So it looks like my little brother is tactically, a very wise player," joked Germany's Melzer.
The other semi-final will see Swiss world No 10 Stanislas Wawrinka take on Frenchman Julien Benneteau.
Second seed Wawrinka edged out Dmitry Tursunov in a hard-fought 2-6 6-3 7-6 (3) win which lasted a lengthy two hours and four minutes while Benneteau outplayed 25-year-old compatriot Adrian Mannarino 6-3 6-3.