Top seed Maria Sharapova was a shock casualty on the ninth day of the French Open after crashing out in the last 16 against fellow Russian Dinara Safina.
Sharapova, playing in her first tournament since her elevation to world No.1 following the retirement of Justine Henin, claimed the opening set on a tie-breaker only to lose her way in the match and conceding a 6-7 7-6 6-2 loss in two hours and 52 minutes.
Safina, the 13th seed, will now face another Russian, Elena Dementieva, for a place in the semi-finals at Roland Garros.
Safina was considered a dark horse for the women's title coming into this event after claiming the biggest win of her career at last month's German Open, where she defeated Henin, Serena Williams and Dementieva en route to the crown.
But she did not make a good start on Suzanne Lenglen Court on Monday, losing the opening set on the tie-break (8/6) after sharing two service breaks with Sharapova.
The Australian Open champion's service game looked rusty in the opening set however, with a number of double faults giving her 22-year-old opponent hope that she could repeat her victory against Sharapova at this same stage of the tournament two years ago.
Sharapova was broken in the first game of the second set as Safina looked for an instant reply, but her momentum was interrupted when the rain clouds once again drifted over Roland Garros and play was suspended for 90 minutes.
When the players returned it looked as though Sharapova's bid for a first French Open crown would remain on track as she streaked 5-2 ahead.
Safina held in the next game before facing down Sharapova in the ninth as the three-time grand slam winner failed to serve out the match.
Both players held the rest of the way to bring about a second tie-break, and again Sharapova got to within an ace of putting the game to bed.
Enjoying a 5-2 lead in the decider, Sharapova lost the plot completely, losing five points in a row - including a costly double fault at 5-3 - to allow Safina to level the match.
Sharapova appeared to have stopped the rot when she broke Safina in the first game of the third, but when the 13th seed broke straight back the 21-year-old appeared to switch off - she even began to show signs of petulance towards the 15,000-strong crowd Suzanne Lenglen Court.
Safina was by now smelling blood, and when Sharapova netted twice on successive points to drop 4-2 behind with another break, it appeared to be a matter of when, rather than if, Safina would send the tournament favourite packing.
Victory arrived two games later when Sharapova fired long trying to rebuff a match point, and while Safina's victory was greeted with warm applause, Sharapova left the arena with boos ringing in her ears.
Earlier, Dementieva had to dig deep to reach the quarter-finals after dispatching compatriot Vera Zvonareva in three sets.
Seventh-seeded Dementieva took the early initiative but let her lead slip before rallying in the third to claim a 6-4 1-6 6-2 victory.
Zvonareva, seeded 11, made a bright start to the opener with two early breaks but Dementieva fought back as her opponent's serve began to break down, eventually going ahead 5-4 before holding to claim the set.
Dementieva laboured in the second, dropping five games in a row as