'S-HERTOGENBOSCH, Netherlands -- No.1 seed CoCo Vandeweghe reached the Libéma Open semifinals on Friday after surviving a nearly three-hour battle with her countrywoman Alison Riske before emerging victorious, 7-6(6), 3-6, 7-6(12).

Two-time Libéma Open champion Vandeweghe had to overcome seven match points held by Riske in the final-set tiebreak before claiming victory on her fifth match point of the tussle. Vandeweghe ultimately powered past Riske by the slimmest of margins, thanks to 16 aces and winning 71 percent of her first service points.

Vandeweghe is still alive in her quest to win a third title in Den Bosch, and her semifinal opponent will be No.7 seed Aleksandra Krunic of Serbia, who ousted Russian qualifier Veronika Kudermetova, 6-2, 6-2, earlier on Friday.

Vandeweghe opened the encounter with three consecutive double faults, which was a harbinger of the curious start to the match. Vandeweghe double faulted a fourth time in the game to drop serve, but that did not cause an immediate problem for her, as it kicked off four straight breaks of serve en route to 2-2. Both players were returning well at this juncture, but also struggled with early unforced errors.

The top seed was the first to find her footing in the opening set, as Vandeweghe blasted two aces to finally hold for 3-2. She raced to a 5-2 lead before Riske held serve for the first time, which caused Vandeweghe to serve for the set at 5-3.

Vandeweghe was broken in that game, however, and Riske followed that up by holding at love to level the set at 5-5. Riske then staved off a set point at 6-5 with a powerful serve, and held once more to send the opening set into a tiebreak.

In the breaker, Vandeweghe charged out to a 6-2 lead, grasping four more set points after a Riske backhand passing shot flew barely long. But after three Vandeweghe unforced errors and one forehand winner by Riske, Vandeweghe’s advantage was completely erased, and they stood at 6-6. There, an ace by Vandeweghe gave her a sixth set point, and that one was converted via a stunning backhand winner into the corner.

It was Riske, though, who clinically moved through the second set with minimal fuss. The World No.63 claimed the sole break of serve in the set at 3-2 after an error-prone Vandeweghe pushed a forehand into the net while down break point.

Riske followed up the break with a hold at love, garnering a 5-2 lead, and two games later, the unseeded American reached triple set point with her second ace of the match. On her second opportunity, Riske hit a solid serve which was returned long by Vandeweghe, evening the match at one set apiece.

The deciding set went with serve reasonably handily until Riske served at 5-4, where Vandeweghe slammed a backhand winner at deuce to clinch a match point. However, the No.1 seed hit three miscues in a row to allow Riske to hold for 5-5. Vandeweghe then had two more match points on Riske’s serve at 6-5, but they were both squandered by poor service returns.

The players advanced to the tiebreak, and after those blown chances by Vandeweghe, Riske took the early initiative in the final stage. A blistering forehand winner down the line put Riske up 5-3, and she held through to 6-4, giving her two match points to complete the upset. But two netted backhands by Riske let Vandeweghe pull the breaker back to 6-6.

An ace by Vandeweghe gave her a fourth match point at 7-6, but Riske held both of her subsequent service points to claim a third match point of her own. Vandeweghe survived that one, and two more, as the tiebreak progressed to 10-10. On that point, a Vandeweghe double fault handed Riske a sixth chance to close out the match, but a rally forehand into the net by Riske pushed the score to 11-11.

On her serve, Vandeweghe saved a seventh match point with a strong forehand to stay level at 12-12, and after a fourth change of ends, another powerful forehand by the top seed gave her a fifth match point. This time, a rally ended with a wide Riske forehand, giving Vandeweghe the relief of outlasting her fellow American in a closely contested marathon.

More to follow...