TIANJIN, China - Timea Bacsinszky's comeback gathered steam at the Tianjin Open with a 7-6(2), 7-6(5) upset of No.4 seed Aryna Sabalenka over two hours and 16 minutes.

The No.329-ranked Swiss player had needed to enter the tournament on a protected ranking, and before this week had not won a match at WTA level for 16 months - since Wimbledon 2017. Having spent six months sidelined due to a leg injury, Bacsinszky lost the first nine matches of her comeback this year, and saw her ranking plummet to No.761 in July.

But last month saw the two-time Roland Garros semifinalist finally get off the ground with a final run at the ITF $80,000 event in Biarritz - and she had defeated Sabalenka in their only previous meeting, a 6-4, 7-5 win in last year's Fed Cup semifinals in Minsk. Bacsinszky's repeat of that result today marks her first WTA semifinal since Roland Garros 2017 - and rules the Belarusian out of contention for this year's BNP Paribas WTA Finals Singapore presented by SC Global.

"Winning two sets in a row against an almost-Top 10 player - for me to be able to keep my focus and my level of play the whole match was really great," enthused a happy Bacsinszky afterwards. "So I'm very proud and very happy."

It is the fifth time that Sabalenka has been defeated by a player ranked outside the Top 100 this year, following losses to Sara Errani in Dubai, Viktoria Kuzmova in Fed Cup play, Maria Sanchez in San Jose qualifying and Varvara Lepchenko in Québec City - but her lowest-ranked defeat since falling to World No.336 Valentini Grammatikopoulou in the first round of an ITF $25,000 event in Minsk in May 2016.

Initially, though, it seemed as if Sabalenka's power would be too much for Bacsinszky. Opening with a flurry of winners off both wings, the Belarusian stormed through the first three games, breaking with a cool-headed counterdrop and coming up with a ferocious backhand down the line to stave off break point in the next game.

For Bacsinszky's part, the 29-year-old was only able to show her best tennis intermittently, with too many cheap errors betraying her rust and long winless drought. But, trailing 2-5, her game finally began to click consistently.

Deploying the full range of her variety and excellent anticipation on defence, the former World No.9 refused to give Sabalenka the same ball twice. Forehand slices were mixed up with high loopers and flat, powerful drives off the backhand side; canny placement forced the New Haven and Wuhan champion to strike the ball from increasingly awkward corners of the court.

Sabalenka's groove had been disrupted and her power blunted, and slowly Bacsinszky clawed her way back into the match. Saving three set points en route - one on return at 3-5 and two on serve at 4-5 and 5-6 - the four-time WTA titlist's clever use of slice enabled her to dominate the tiebreak, finishing the set with a sharp backhand angle that Sabalenka had no reply to.

Starting the second set with a backhand pass off a Sabalenka smash, Bacsinszky was eager to maintain her momentum. Though a handful of loose errors conceded the first break to Sabalenka in the third game, Bacsinszky snuffed out any immediate hopes of a comeback by breaking back to love in the next game, including one of several magnificent off backhand winners.

Thereafter, the two-time Wimbledon quarterfinalist came up with several plays that were a reminder of how much of an asset her style is to the Tour: a low forehand pass followed by a pinpoint lob that left Sabalenka stranded at net in the sixth game, a dropshot-pass combination in the ninth game that was so good her opponent also had to applaud.

Sabalenka's firepower meant that the 20-year-old could never be counted out of the match - and although Bacsinszky's variety would elicit several errors, the improved consistency in her game meant that Sabalenka never lost control of her power for any extended period of time.

Instead, it fell to the 2015 Beijing runner-up to call upon her most clutch play in order to close her opponent out. At 4-4, strong serving saved a break point; at 5-5, Bacsinszky came through four deuces for a crucial hold, never allowing Sabalenka to reach break point and sealing the hold with a lob that the World No.11 could only send into the net.

Though Sabalenka responded with a clutch hold of her own to force a tiebreak, despite an extremely entertaining scrambling Bacsinszky point that ended with Sabalenka sending a volley wide, it was the comeback player who again proved sharper in the deciding game. Sabalenka would go down fighting, smacking two breathtaking backhand winners down the line to keep herself in contention - but, just as in the first tiebreak, also coughed up a double fault that proved significant. By contrast, Bacsinszky would find her second ace of the day to move ahead, and capture victory on her second match point as a deep, defensive backhand caught Sabalenka flat-footed on the baseline. A yelp of joy showed just how much the win meant to Bacsinszky - as did the tears that flowed when she sank into her chair.

Bacsinszky discussed afterwards how much it meant to her to be playing at a high level again. "I'm even looking forward to my off-season preparation," she exclaimed. "Normally players say, oh, it's so tough - but it's because I'm so happy to be playing again." First, though, her end-of-year schedule will take her to France, where she has two ITF tournaments in Poitiers and Nantes lined up before the Limoges WTA 125K. 

Bacsinszky's fitness is holding up so far, too: "I'm feeling some parts of my body are a little overused, especially because I haven't been playing at that level for so long, especially two days in a row,  she admitted.

"But overall I must say for a 29-year-old body I feel pretty OK, so I must thank my physical coach for making me fit again."