Top seed Tomas Berdych crashed out of the ATP Chennai Open on Friday on a night of dramatic upsets that saw third seed Marin Cilic and number four Stanislas Wawrinka also bow out.
Berdych, the world number six from the Czech Republic, was stunned by the 80th-ranked Roberto Bautista Agut of Spain, who won 7-5, 2-6, 6-3 to storm into his first ATP semi-final.
The 24-year-old Agut, one of the 13 Spaniards to finish in the top-100 last year, showed no signs of nerves as he served and volleyed superbly to beat the tournament favourite in two hours and 17 minutes.
"This is of course my biggest win on the tour," said Agut, who was playing in only his second ATP quarter-final. "I am happy to make such a good start in the first week of the season."
Agut's semi-final opponent on Saturday will be 47th-ranked Benoit Paire of France, who knocked out world number 15 Cilic 6-4, 1-6, 7-5 earlier on Friday.
Paire, who had never beaten a top-20 player before, said he looked forward to the semi-final.
"There are no easy matches on the circuit, especially a semi-final," he said. "I have to prepare well for it."
Wawrinka was waylaid by 23-year-old Aljaz Bedene of Slovenia, who advanced to his maiden ATP semi-final with a 6-2, 7-6 (8/6) win in an hour and 31 minutes.
The 86th-ranked Bedene will clash with world number nine Janko Tipsarevic of Serbia for a place in the final of the $430,000 season opener.
Second seed Tipsarevic, the only survivor among the top four pre-tournament favourites, swept aside eighth seed Go Soeda of Japan 6-2, 6-4.
Tipsarevic, who lost last year's Chennai final to Canada's Milos Raonic, said he was satisfied with his match against Soeda.
"I think I served good and also returned well," he said. "To lose just six games in the whole match means I played well. But one has to keep improving all the time and that is my aim."
Tipsarevic, asked about his unfamiliar semi-final opponent, said: "Bedene is a very promising young player with a fine serve. I played him once before, but he got injured, so I really have not seen enough of him."
Cilic, a two-time Chennai Open winner in 2009 and 2010, said it was not easy to tackle a "flashy" player like Paire.
"Benoit is different from other players because his game is so flashy," the Croat said. "He comes up with great returns when least expected and that took me by surprise.
"He played the first set very well, and after I took the second, it was a cat and mouse game with each of us trying to outwit the other. But he was so much better than me in the last few games.
"I obviously need to lift my game if I am to do well this year. But this is just the start of the season and hopefully I will be back to my best soon," said Cilic.