Moscow - Qualifier Edouard Roger-Vasselin saved four match points as he stunned top seed Alexandr Dolgopolov of Ukraine 6-3, 5-7, 7-6 (8/6) in the second round of the Kremlin Cup on Thursday.
The 116th-ranked Frenchman forced a tie-break after saving two match points on his serve in the 12th game of the third set.
In the tie-break Roger-Vasselin recovered from 6-4 down to win the last four points, sealing victory when his opponent's forehand went long.
Roger-Vasselin reached his third quarter-final of the year and now plays Croatian Ivo Karlovic or Russian Alex Bogomolov on Friday.
Second seed Andreas Seppi of Italy and fourth-seeded Brazilian Thomaz Bellucci also went through.
Seppi beat Dutchman Igor Sijsling 7-5, 6-2 and Bellucci eliminated Italian Flavio Cipolla 6-4, 6-1.
In the women's event, fourth-seeded Serbian Ana Ivanovic booked her spot in the last eight with a routine 6-1, 6-4 win over Russian qualifier Valeria Solovieva.
"I think she looked nervous, especially in the first set, because it was probably her first big match," former world No 1 Ivanovic told reporters.
Ivanovic next meets 158th-ranked compatriot Vesna Dolonc.
Moscow-born Dolonc, who took Serbian citizenship last year, crushed Romanian Simona Halep 6-1, 6-0 to reach her first quarter-final on the WTA Tour this year.
Australian Samantha Stosur, the top seed, begins her campaign against France's Alize Cornet later on Thursday.