STUTTGART, Germany – No.1 seed Agnieszka Radwanska extended her winning streak against Karolina Pliskova, dispatching the Czech 6-2, 7-6(8) to claim the last semifinal spot of the Porsche Tennis Grand Prix.

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Despite Pliskova’s powerful weapons and game, crafty Radwanska has claimed all five of their previous encounters in straight sets, allowing the Czech no more than five games a set. Their last clay court encounter ended in a smooth 6-3, 6-4 victory for Radwanska.

After Radwanska took the first set in a quick half an hour, it seemed like their Stuttgart quarterfinal match would go the same way as all their previous ones. Radwanska was unbothered by Pliskova’s famous serve, and so long as she got back a return she found a way to control the rallies and give the Czech the type of low, sliced balls that trouble her the most.

But instead of shrinking away in the second set, Pliskova instead gave Radwanska a taste of her own medicine, catching her with drop shots and beating her at the net. She broke Radwanska’s serve at 2-3, and survived a rollercoaster 11-minute game to consolidate it.

Despite the monumental effort it took for Pliskova to get the lead, it was short-lived Radwanska quickly broke back and leveled the match at 4-4. They kept toe to toe until another marathon game – this time 15 minutes long, as Radwanska tried to hold serve and subdue the resurgent Pliskova who brought up seven break points – sent the match into a tiebreak. Four match points later, Radwanska was through to her fifth semifinal of the year.

Awaiting Radwanska in the final four is German qualifier Laura Siegemund, who extended her own streak of upsets to oust the No.6 seed Roberta Vinci 6-1, 6-4 and reach her first WTA Premier-level semifinals.

The Stuttgart native felt strong support from the German crowd who were out in full force to support their local underdog.

“That was a crazy mood out there,” Siegemund said of the animated Porsche-Arena crowd. “It has so fun. I was very focused during the match and tried to concentrate on my game, but I could hear them in the background – the stadium was shaking.”

With the win she’ll reach a new career-high ranking of No.55, and earn herself a spot in German tennis history, too. With Angelique Kerber also having reached the semifinals earlier in the day, this marks the first time since 1985 that two Germans have reached this stage in Stuttgart.