Madrid - Serena Williams's stunning 27-match winning streak was snapped in resounding fashion by Petra Kvitova on Friday as the Czech progressed to the Madrid Open final 6-2, 6-3.
Kvitova will face Russia's Svetlana Kuznetsova in Saturday's final after she also pulled off a big upset in beating defending champion Maria Sharapova 6-2, 6-4.
However, there was no such upset for home favourite and four-time champion Rafael Nadal as he moved into the semi-finals with a 6-3, 6-4 win over Grigor Dimitrov.
Andy Murray is also safely into the semi-finals for the first time in Madrid on clay as he overcame a hobbled Milos Raonic 6-4, 7-5.
Kvitova has only recently returned to the tour following a two-month break after admitting to feeling physically and mentally exhausted, but she looked the fresher player in wrapping up victory in just over an hour on court.
"I was very slow off the mark. After my serve I wasn't moving as well as I should have. I wasn't in it, I wasn't Serena today," said 19-time major winner Williams.
Wimbledon champion Kvitova reeled off four consecutive games from 2-2 to take the first set.
She then moved 5-1 up in the second as the Czech went on to seal her first victory over Williams in six attempts.
"It is a special day for me and I am happy it is in a semi-final here in Madrid so I can play the final," said Kvitova.
Kuznetsova also kept her fairytale return to form going as she scored her first victory over Sharapova in seven years to reach her first premier mandatory final since 2009.
"This week I was fighting. I was a little bit lucky in some moments," said Kuznetsova.
Defending champion Sharapova was the heavy favourite to reach the final for a third consecutive year.
However, it was the two-time Grand Slam champion Kuznetsova who dictated and didn't drop her serve once in the match.
"I don't think it caught me by surprise. I'm playing in a semi-final of a tournament, you have to be ready for it. She was just the better player," said Sharapova.
Nadal had warned that his form on the clay after failing to win a title since the European season began in Monte Carlo and Barcelona would be put to the test by Dimitrov and the Spaniard looked back to his old self on his favoured surface.
He won five of the last six games to set up a semi-final meeting with Czech Republic's Tomas Berdych.
Sixth seed Berdych saved a match point in the second set before seeing off giant American 16th seed John Isner 3-6, 7-6 (9/7), 7-6 (7/1).
"I played a complete match, apart from two games in the second set when my intensity dipped a little," said Nadal.
"I am very happy, very satisfied and it is a great result to be in the semi-final. I have passed an important test."
One break in each set was enough to continue Murray's perfect start to the clay court season after winning his first tournament on the surface earlier in the week in Munich.
Raonic has withdrawn from Rome next week and seemed to still be struggling with the foot problem that forced him to pull out of the Monte Carlo Masters last month as Murray used a series of drop shots to good effect.
"Certainly (his injury) altered the way I played the match a little bit," said Murray.
"I felt when I was serving I played the match well. I made him do a lot of moving. He seemed to be moving okay from side to side, but it was moving forward that was causing him the issues."
The Scot will next face Japanese fourth seed and 2014 runner-up Kei Nishikori who demolished David Ferrer 6-4, 6-2 in just 72 minutes.
Results from the seventh day of the ATP and WTA Madrid Open on Friday (x denotes seeded player):
Svetlana Kuznetsova (RUS) bt Maria Sharapova (RUS x3) 6-2, 6-4
Petra Kvitova (CZE x4) bt Serena Williams (USA x1) 6-2, 6-3
Tomas Berdych (CZE x6) bt John Isner (USA x 16) 3-6, 7-6 (9/7), 7-6 (7/1)
Rafael Nadal (ESP x3) bt Grigor Dimitrov (BUL x10) 6-3, 6-4
Kei Nishikori (JPN x4) bt David Ferrer (ESP x7) 6-4, 6-2
Andy Murray (GBR x2) bt Milos Raonic (CAN x5) 6-4, 7-5