Taiwan’s Hsieh Su-wei yesterday crashed out of the second round of the singles at the Pan Pacific Open, then teamed up with younger sister Hsieh Yu-chieh to advance to the quarter-finals of the doubles.

Despite a spirited second-set fightback, the Taiwanese No. 1 fell to a 6-3, 1-6, 6-2 defeat to Belgian ninth seed Elise Mertens in 1 hour, 53 minutes in Osaka, Japan.

World No. 33 Hsieh Su-wei converted six of 10 break points, four in the second set, but saved only five of 12 as she failed to take advantage of her opponent’s six double faults.

The victory improved the Belgian world No. 24’s career record over Hsieh to 2-1 and saw her advance to a quarter-final against the winner of today’s second-round clash between Sloane Stephens of the US and Italy’s Camila Giorgi.

Hsieh Su-wei then returned to the court with her sister and battled through the first set against Alicja Rosolska of Poland and Dayana Yastremska of Ukraine before cruising through the second for a 6-4, 6-0 victory in 55 minutes.

The sisters saved six of seven break points and converted two of six to set up a quarter-final today against top seeds Anna-Lena Groenefeld of Germany and Demi Schuurs of the Netherlands.

Fellow Taiwanese sisters and second seeds Chan Hao-ching and Latisha Chan are also to play their quarter-final today against Gabriela Dabrowski of Canada and Caroline Garcia of France.

In yesterday’s other singles matches, fourth seed Angelique Kerber returned to her winning ways after a five-match losing streak with a 6-2, 6-4 victory over American qualifier Nicole Gibbs.

“It’s nice to have a win again,” the German told the WTA Web site. “The goal now is to finish the year as well as I can, to put all the energy which I have into this run in Asia and to play well in the next few weeks.”

Japanese top seed Naomi Osaka defeated Bulgarian qualifier Viktorija Tomova 7-5, 6-3, while fifth seed Madison Keys of the US battled back to beat Kazakh qualifier Zarina Diyas 5-7, 6-0, 6-4.