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 semi-finalist, 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.