Lucie Safarova reached the final of the French Open in 2015 but suffered a third-round exit at the hands of Samantha Stosur on Friday, while Petra Kvitova was stunned by Shelby Rogers.
After starting the year with five straight defeats, Safarova won the Prague Open in April to boost her confidence as she looked for another strong run at Roland Garros.
However, the world number 13 was defeated by Stosur 6-3 6-7 (0-7) 7-5, and there was disappointment for Kvitova too as she suffered a shock exit at the hands of Rogers - the 108th ranked American progressing by an unusual 6-0 6-7 (3-7) 6-0 scoreline.
Internazionali d'Italia winner Simona Halep and Agnieszka Radwanska came out on top in three-set matches, but Garbine Muguruza had no such trouble as she surged past Yanina Wickmayer.
SAFAROVA AND KVITOVA DUMPED OUT
Two former French Open finalists in Safarova and Stosur came together in the third round, and it was the Australian who came out on top.
A break in the final game enabled Stosur to pick up just a fourth win in 15 meetings with the Czech, setting up a match against Halep for a place in the quarter-finals.
After losing the first set to Rogers 6-0, Kvitova showed great resilience to battle back and take the match the distance. However, the two-time Wimbledon champion was bagelled by the American once again, resulting in a surprise exit.
MUGURUZA MARCHES ON
A nine-game winning streak against Wickmayer helped Muguruza cruise into the next round by winning 6-3 6-0, but the Spaniard is not getting carried away with her impressive form.
"The more matches you get to play, the more you realise that winning time and again is possible, and with that confidence, you can actually organise your game," said Muguruza.
"Winning matches is what I want, but of course from now on I'm just going to play things match by match."
RADWANSKA SWEARS BY MOTIVATION TECHNIQUE
After cruising into a one-set lead, Radwanska let a 3-0 lead in the second slip away and Barbora Strycova forced a decider by coming out on top in a tie-break.
The second seed fought back, ensuring the world number 33 did not build any momentum and completing a 6-2 6-7 (6-8) 6-2 win.
Asked how she motivated herself to recover from letting the second set slip away, Radwanska said: "I was just saying bad words to myself. That helps."
HALEP STAGES COMEBACK
Despite taking a 4-2 lead in the opening set, Halep suffered a pair of breaks as she lost four straight games to surrender the first set to Japanese teenager Osaka.
Unforced errors and began to creep in for the world number 101, whose service game also slackened, and Halep pounced to force a decider.
The Romanian - a French Open runner-up in 2014 - saved two break points but dropped her serve after taking a 3-1 lead in the third set. She was unperturbed by the set-back, though, and motored on to victory.