SHENZHEN, China - No.8 seed Elina Svitolina may have had her place at the top of the Shiseido WTA Finals Shenzhen Purple Group sewn up already, but she wasn't about to rest on her laurels in her final round-robin match, coming from a break down in both sets to post a 7-5, 7-6(10) win over alternate Sofia Kenin in two hours and 10 minutes.

"Each time I step on the court I have to win," Svitolina confirmed afterwards - a trait inculcated in her by her family. "My parents raised me this way - that I have to fight for everything, I have to give 100% each time I play," she continued. "They would be very angry if I would just give this match to her. And my grandmother, as well - she would be very sad."

The pair have put together one of the most tightly contested rivalries of 2019, with nothing in their two wins apiece coming easily - and today's result cleaved to the same pattern as the Ukrainian maintained her unbeaten record this week to edge ahead 3-2 in the head-to-head. Having started the group stages by triumphing in the longest tiebreak of the WTA Tour season, a 14-12 epic over Karolina Pliskova, Svitolina would end them by winning the joint second longest, a dramatic 12-10 decider that she finally took on her sixth match point - and, naturally, she drew on the first experience to get through the last.

"I already had similar experience in the first match here," she said afterwards. "I knew that I had to stay strong. There was no other way. I had no other option. That's pretty much what helped me to win."

Svitolina, deploying a more aggressive first-strike strategy, tallied 11 aces and 25 winners for the day - but still needed to draw on her trademark grit to reel Kenin in over the course of a first set in which the defending champion trailed almost all the way. The American's superior intensity out of the blocks garnered her the first break and a quick 3-1 advantage - but thereafter Kenin squandered numerous opportunities to build a more unassailable lead, with six double faults proving costly.

Two points for a 4-1 double break went begging - the first on a dead net cord for Svitolina - as did two to hold for 4-2 as the 20-year-old lapsed into error to concede her own serve. Though Kenin regained the break immediately, her forehand went awry when it came to serving out the set - while Svitolina, as the set progressed, was growing in confidence, taking one drive volleys with aplomb and at one stage serving a trio of aces to hold.

The Wimbledon and US Open semifinalist's hustle was on full display in the two games that ended the first set and opened the second. Both times, Kenin sprang out to a 40-0 lead; both times, Svitolina came up with some of her finest serving, defence and creativity to steal the game from under her opponent's nose. Chasing down a Kenin dropshot would seal the opening act; a brilliantly timed clean dropshot winner of her own would save a fourth break point in the next game en route to the hold.

A series of well-played holds ensued, with both players coming up with quality ballstriking - and some more spectacular retrieving from Svitolina. Despite this, Kenin held firm to stave off a break point with a backhand one-two punch to hold for 4-4 - and immediately made her move on the former World No.3's serve, unleashing a few more brilliant backhands to break for 5-4.

But as in the first set, the three-time WTA titlist was unable to close the deal in a dramatic tussle that tilted back and forth. Kenin even held set point this time round - only for her 10th and 11th double faults to hove, unwanted, into view. Svitolina, whose intensity had slightly dipped in the previous passage of play, lit up again, nailing a backhand pass at full stretch and drawing errors with deep returns, eventually taking her fourth break point to level at 5-5.

In contrast to Kenin's service woes, Svitolina's delivery would be one of her greatest weapons today - as she demonstrated superbly in the closing stages of the match. Two aces and two service winners took her to 6-5, and the 25-year-old would hammer down another two in the ensuing tiebreak.

Nonetheless, Kenin - who has been raring to go all week - was keen to extend her WTA Finals on-court experience, and battled valiantly in a gripping extended dénouement. Despite being plagued by double faults and 45 unforced errors, the Toronto and Cincinnati semifinalist came up with the goods with her back to the wall to save one match point serving at 5-6, and another four in a gripping tiebreak - two with perfectly conceived and executed dropshots, another with consecutive down-the-line strikes to end a 23-shot rally and another with a bold drive volley.

However, Svitolina would be undeterred from her mission - and, coming full circle in her round-robin journey, ended as she had begun: by showing the supreme resolve needed to edge a marathon tiebreak, this time capturing her sixth match point as a final Kenin forehand found the net.

Tomorrow, Svitolina will bid to keep her WTA Finals winning streak going against No.7 seed Belinda Bencic in her sixth semifinal of 2019. "We know all the game style that she has," said Svitolina. "She takes the ball quite early, and you have to be ready for this game style. For me the main thing is to recover first, to be fresh tomorrow physically and mentally."