Timea Bacsinszky ended Aryna Sabalenka's hopes of qualifying for the WTA Finals with a quarter-final victory in the Tianjin Open as Karolina Pliskova stayed on course for Singapore.

Bacsinszky lost nine matches in a row on her return from a six-month absence due to a leg injury but has found form late in the season.

The two-time French Open semifinalist, down at 329 in the world rankings, reached the final of an ITF event in Biarritz last month and showed she is back in business by beating Sabalenka 7-6 (7-2) 7-6 (7-5) on Friday.

Bacsinszky was a break down in both sets but battled back against the powerful fourth seed, mixing up her tactics shrewdly.

The Swiss was reduced to tears after coming out on top in a second tie-break, ensuring Sabalenka's late charge for a WTA Finals spot came up short.

Pliskova occupies the eighth and final spot in the Race to Singapore and the top seed added to her points tally with a hard fought 5-7 6-0 6-3 win over Katie Boulter.

The former world number one will face Bacsinszky in the last four, having twice come from a break down in the final set to end unseeded Brit Boulter's impressive run in the tournament.

Caroline Garcia and Su-Wei Hsieh will contest the other semi-final after Petra Martic and Elise Mertens both retired when trailing in the second set after losing the first.