World number one Simona Halep and defending champion Caroline Garcia suffered second-round defeats while Elina Svitolina and Karolina Pliskova also made early exits at the Wuhan Open on Tuesday.

Halep received treatment on her back and left thigh before succumbing 6-0 7-5 to Dominika Cibulkova in the top seed's first match since losing to Kaia Kanepi in the opening round of the US Open.

Garcia will not be repeating her success of last year in China after Katerina Siniakova consigned the fourth seed to a 3-6 7-6 (7-5) 7-6 (7-4) defeat, the qualifier saving a match point in the second set before going on to pull off a shock.

Svitolina, the sixth seed, went down 6-4 2-6 6-1 to Aryna Sabalenka, while Pliskova and Kiki Bertens were knocked out after winning the Tokyo Open and Korea Open respectively last weekend.

Madison Keys retired from her match against Angelique Kerber at 6-0 4-1 down due to a knee injury on a day which saw Caroline Wozniacki, Petra Kvitova and Garbine Muguruza reach round three.

CIBULKOVA MAKES HAMPERED HALEP SUFFER

Halep injured her back during a training hit on Sunday and the French Open champion was clearly not fully fit as she suffered the humiliation of a first-set bagel.

Cibulkova showed no mercy on the hampered Romanian, who could only muster one winner in the opening set.

Halep appeared to benefit from a couple of medical timeouts as she fought back from 2-0 down in the second to lead 4-2, but the Slovakian cut down the unforced errors to avoid a decider, sealing victory after midnight.

Cibulkova will take on Daria Kasatkina - a winner over Halep in the second round of this tournament last year - in the third round.

BATTLING SINIAKOVA HANGS IN THERE TO TOPPLE GARCIA

Garcia, who became the first player to be crowned champion in Wuhan and Beijing back-to-back last year, paid the price for not being able to put Siniakova away in the second set.

The world number four from France had the opportunity to serve out the match, but failed to do so and squandered a 3-1 lead in the third before losing a tie-break.

"It was such a long battle, I'm very happy that I won," said Siniakova, who will now go up against Muguruza. "[Garcia and I] have already played a few times and every time it's three sets. Every time I played her it was really long and tough match, so I was expecting a tough one."

SURGING SABALENKA SEES OFF SVITOLINA

Sabalenka proved just how dangerous she can be once again by claiming the scalp of Svitolina.

The unseeded Belarusian secured a seventh top-10 win of the season after giving eventual champion Naomi Osaka a big test in the fourth round of the US Open.

"I've not been counting! [her wins over players in the top 10] It's always special to beat top players. I'm so happy with this result," said Sabalenka.

PLISKOVA AND BERTENS BROUGHT BACK DOWN TO EARTH

Pliskova was on a high after beating Osaka in her homeland to win the title in Tokyo on Sunday, but the eighth seed was stunned 6-1 3-6 6-3 by new Chinese number one Wang Qiang two days later.

Bertens wrapped up her third title of the year in Korea, but Anastasia Pavlyuchenkova saw off the world number 11 with a 6-4 6-2 success.

Both Pliskova and Bertens are battling to seal spots in the season-ending WTA Finals in Singapore.