Little-known Pole Jerzy Janowicz continued his brilliant run at the Paris Masters on Friday, reaching the semifinals when eighth seed Janko Tipsarevic retired.
Serb Tipsarevic, who had on Thursday claimed the last spot for next week's World Tour Finals in London, withdrew when trailing 3-6, 6-1, 4-1 and having called the trainer on a game earlier.
Organisers said he had been suffering from fatigue from the end of the first set.
While the crowd booed Tipsarevic, world number 69 Janowicz celebrated becoming the first qualifier to progress to the last four at the event since 2004.
The unseeded Janowicz, who eliminated world number three Andy Murray on Thursday, showed signs of nerves at the beginning of the match against Tipsarevic and dropped his serve in the second game.
However, the Pole's mix of raw power from the baseline and cunning drop shots eventually wore down the Serb who simply ran out of ideas.
The 21-year-old Janowicz next faces Frenchman Gilles Simon who advanced with a 6-4, 6-4 win over Czech fifth seed Tomas Berdych.
The unseeded Simon, who reached the quarterfinals after Japanese Kei Nishikori withdrew due to an ankle injury, had too much pace for Berdych in front of his home crowd.
Simon was 4-1 down in the second set but fought back to win five games in a row, wrapping up the contest with an ace on his second match point.
The other two quarterfinals will feature Frenchmen Jo-Wilfried Tsonga, the eighth seed, and Michael Llodra against Spain's David Ferrer and American Sam Querrey respectively.