US Open champion Flavia Pennetta was eliminated by a player 408 places below her in the world rankings in a major first-round upset at the Tianjin Open.

Ukrainian qualifier Lyudmila Kichenok ousted the top seed in straight sets in China to claim by far the biggest win of her career.

Kichenok broke serve twice to win the first set and took her fifth break point of the second set to lead 3-2.

Pennetta broke back to level at 5-5 but the world number 414 won two games in succession to complete a superb 6-3 7-5 win.

Third seed Karolina Pliskova needed more than two hours and 10 minutes to battle past Slovakia's Kristina Kucova in three sets.

Pliskova dropped the opening set and squandered one set point in the second with a double fault before closing it out.

The Czech then broke at a crucial moment to lead 6-5 in the decider but went down 15-40. She saved both break points, the first with an ace, and though she double-faulted to hand Kucova another she again held firm and finally sealed victory.

Agnieszka Radwanska, seeded second, had no such worries as she breezed past qualifier Olga Savchuk 6-0 6-1, while her sister Urszula beat Kichenok's twin Nadiia 6-4 6-0 after an early scare.

Nadiia Kichenok broke in the second game but gave it straight back with a double fault, before recovering from a break down later in the set.

Urszula Radwanska produced a decisive third break, though, before breezing through a one-sided second set.

Timea Babos hammered Alla Kudryavtseva 6-0 6-1, Danka Kovinic won 6-4 6-1 against Kateryna Bondarenko, Bojana Jovanovski beat Ons Jabeur 6-7 (1/7) 7-6 (7/4) 6-1 and Chinese wild card Ying-Ying Duan was a 6-3 6-3 winner over Nicole Vaidisova.