ZHUHAI, China - No.1 seed Kiki Bertens drew on all of her reserves to come through an arduous 7-6(5), 6-2 win over No.8 seed Donna Vekic in one hour and 59 minutes to open the Azalea Group at the Hengqin Life WTA Elite Trophy Zhuhai.

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The pair have delivered some of this season's most dramatic highlights across the continents and seasons: Vekic saved two match points to oust Bertens in the second round of Brisbane 7-6(5), 1-6, 7-5 in the first week of the year, but would be unable to close out their Beijing opener three weeks ago despite serving for it, with Bertens squeezing through 3-6, 6-1, 7-6(3). In between, the Dutchwoman captured her maiden indoor title in St Petersburg by beating Vekic 7-6(2), 6-4 in the final - and today, emerged victorious for a third consecutive time to take a 4-3 lead in the overall series.

Over the course of the one-hour, 20-minute opening act, there was little between the two competitors until the very end. The first four games alone took 28 minutes to complete - and at the end of this passage of play, it was Vekic who had the upper hand. Unleashing the full ferocity of her forehand and finishing points superbly at net, the Croat had broken Bertens in the opening game and then toughed out two mini-epic holds - both of which had ended after four deuces with Bertens netting easy putaways on the drive volley and overhead.

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But the Madrid champion, playing her seventh consecutive week across two continents after attempting to chase down a spot at next week's Shiseido WTA Finals Shenzhen, did not dwell on either the disappointment of failing in that quest or in her poor start today.

"I really had that goal in mind and now it was a little bit gone," as Bertens put it afterwards when discussing how she is continuing to push herself. "But still, once I'm on court I want to win - and this tournament. I still want to win. [It's] really in me that I always want to win, so I think that's my drive."

This came through as she gathered herself superbly for the battle to come back, withstanding Vekic's rampant shotmaking to focus on executing the basics on key points. A first ace staved off a point for Vekic to go up a double break, with a neat forehand angle sealing that hold - and when the US Open quarterfinalist carelessly lost control of her forehand in the next game for Bertens to get back on serve, the 27-year-old needed little further encouragement to turn the match into a battle of wills - and serves.

Bertens' renowned delivery was crucial to her comeback. Under pressure again in the seventh game, she would save three break points - two with simple one-two punches - and close out the hold with three consecutive service winners to move ahead for the first time.

Although both players were now sufficiently grooved on serve to post five straight holds without another break point hoving into view, it was again Bertens who out-competed Vekic on the biggest points to squeeze through the tiebreak. Down 4-5, the 2016 Roland Garros semifinalist came up with a brace of brilliant backhands down the line - the second a pass off a rather tentative Vekic approach - before an errant Vekic forehand sealed the set.

"The first set was really tight, so it was just a few points here and there," recalled Bertens afterwards. "I just was trying to push myself all the time. It was tough, I would say, mentally but also physically. We were both struggling, I think, a little bit. But from 5-4 down I played two really good points."

That wing, so electrifying in the early stages, would be largely responsible for the 23-year-old falling away abruptly in the second set. Unable to find the court with it when she most needed to, Vekic dropped serve three times in a row - twice from game point up - while making an ever-decreasing impact on the Bertens serve to fall behind 0-5.

Bertens, meanwhile, continued to rack up the aces, tallying eight in total, as well as showcasing some remarkable defensive play. There would be a minor stumble at the finishing line as Vekic managed to break and get two games on the board - but at the second attempt to serve out the win, Bertens was impeccable in sending down booming first serves to post a love hold.