WASHINGTON DC, USA - No.4 seed Hsieh Su-Wei continued her successful debut at the Citi Open on Thursday, slicing past Russian qualifier Varvara Gracheva to book her spot in the quarterfinals.

Hsieh was made to work against Gracheva, who was contesting just her second WTA main draw in her career. But the last seed left standing in Washington DC found her way back from the brink to complete the 7-5, 4-6, 7-6(6) victory in a marathon two hours and 43 minutes.

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"She was giving me some pressure, and I gave myself some pressure," Hsieh explained to press after the match. 

"So I tried to handle the pressure on the court, and sometimes I did manage it, but sometimes she'd get me. It was so much up and down." 

Despite the heartbreaking defeat, there are still plenty of positive signs for the Russian: a former Junior Top 20 player, 19-year-old Gracheva won her first ever WTA main draw match at this tournament and, as a result of her ITF-level success, has secured herself a Top 200 debut next week. 

For Hsieh, it was a scenic route toward reaching her second career WTA quarterfinal on US soil. Gracheva got off to a dream start against Hsieh, hitting her targets as the unforced errors rolled off of the Chinese Taipei player’s racquet. She quickly got ahead to an early break for 3-0 lead.

But just as quickly, Hsieh was right back in it, her signature brand of slice and spins vexing Gracheva as she worked her way back. They traded breaks, with Gracheva staying ahead and opening up a daunting 5-2 lead, but Hsieh continued to patiently chip away at her opponent.

As Hsieh grew in confidence Gracheva faltered, and the No.4 seed quickly pulled herself back to level the score at 5-5, breaking the Russian while she was serving for the set. Her trademark double-handed backhands and forehands continued to trouble Gracheva, and another break to Hsieh sealed the opening set. 

Hsieh carried her momentum to win seven games in a row, starting the second set with a 2-0 lead. But Hsieh struggled to put away the Russian teenager, despite leading by a break twice in the set. Gracheva fought her way back both times, leveling the score at 2-2 and breaking back to 4-4 to get them back on serve. She reeled off the last two games to run away with the set, forcing a decider. 

But just as Hsieh looked to have righted the ship, starting with an early break to lead 3-1, it all started to turn as the Russian found some lights-out tennis to rally back to 3-2. From there, they were level through the seven consecutive breaks of serve that followed, Hsieh having served for the match twice. 

In the tiebreaker, Hsieh needed three match points to put away Gracheva as the Russian kept on fighting, but finally closed out the match after over two and a half hours on court. 

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"I was not thinking too about [the other match points]," she said. "I was thinking that it's very important at 6-6, because I wasn't holding my serve in that final set.

"So I was like, 'Yeah, I got a point! Now the next one, I need to make it!' And I make it."

Through to her fifth WTA quarterfinal of the year, Hsieh will take on another young up-and-comer in American wildcard Catherine McNally. The 17-year-old took down her countrywoman Christina McHale, 6-3, 1-6, 6-3 to advance.