HOUSTON, TX, USA – Anhelina Kalinina scored a major upset at the Oracle Challenger Series in Houston as she defeated No.1 seed Danielle Collins, 6-0, 3-6, 6-3.

Playing in her first match since announcing a diagnosis of rheumatoid arthritis, the American struggled to gain her rhythm and dropped the opening set without taking a game, though she fought back and forced a decider before going down in two hours 12 minutes.

The opening set was one-way traffic in favor of the WTA World No.161 as she restricted her opponent to just seven points in the entire set.

Collins fought back valiantly in a second that swung first in her advantage before seemingly heading the way of her opponent. Ultimately, though, it was the WTA World No.31 who took it, fighting back from a break behind.

The third, meanwhile, proved to be a protracted affair, with long games and 23 break points shared between the players.

Collins had four chances to win the opener against the serve but was unable to convert. She then held in the only game in which there was not a single break point, before squandering another three in the third.

Kalinina took the advantage thereafter, with a run of five successive breaks leaving her to serve for the match. Even this proved no simple task as she had to save four more break points before sealing her spot in the last 16.

Elsewhere in the top half of the draw, Katarina Zavatska and Stefanie Voegele, seeded 4 and 7 respectively, won through in three sets against Jessika Ponchet and Fanny Stollar. Usue Maitane Arconada, meanwhile, defeated Hanna Chang without dropping a game in 48 minutes.

In the bottom half of the draw, No.2 seed Taylor Townsend had too much for Anna Danilina, with the WTA World No.84 winning through, 6-2, 6-4.

There was more American success as Bethanie Mattek-Sands took just 40 minutes to beat compatriot Allie Kiick without dropping a game.

Irina Falconi, meanwhile, overcame lucky loser Quinn Gleason in three sets to complete the last-16 line-up.

Happy retirement, Dominika Cibulkova!