Veronika Kudermetova upset top seed Elina Svitolina in the second round of the Kremlin Cup and Jelena Ostapenko fought back to knock Elise Mertens out of the Luxembourg Open on Thursday.

Kudermetova came out on top in her first match against a top-five opponent, defeating Svitolina 6-1 2-6 7-5 in Moscow.

The 22-year-old Russian wrapped up the opening set in only 28 minutes and came from 2-0 down in the decider to move into the quarter-finals.

Kudermetova's attacking approach paid off, world number four Svitolina showing resolve in the final set but missing out on a last-eight showdown with Anastasia Pavlyuchenkova.

Second seed Kiki Bertens advanced with 4-6 6-3 7-5 victory over Kaia Kanepi, while Pavlyuchenkova won an all-Russian contest with Varvara Gracheva 5-7 6-4 6-2.

Kristina Mladenovic will face Bertens after battling her way past sixth seed Anastasija Sevastova 7-5 3-6 6-3.

The top seed also bowed out Luxembourg, with Ostapenko digging deep to see off Mertens 4-6 6-2 6-2.

Ostapenko, runner-up to Coco Gauff at the Linz Open last weekend, will now come up against Antonia Lottner, who went through when Andrea Petkovic retired with a knee injury after losing the first set 6-1.

Defending champion Julie Goerges saw off Sorana Cirstea 4-6 6-4 6-4, while Anna Blinkova and Monica Puig also made it through, defeating Kristyna Pliskova 7-6 (7-5) 3-6 7-6 (8-6).