NEW YORK, NY, USA -- An all-unseeded semifinal is set up in the US Open women's doubles tournament, as upsets abounded on Sunday in Flushing Meadows.

Laura Siegemund of Germany and Vera Zvonareva of Russia ended the title defense of No.2 seeds Elise Mertens of Belgium and Aryna Sabalenka of Belarus, claiming a 6-4, 7-6(1) victory over the 2019 champions in an hour and 40 minutes.

In the final four, Siegemund and Zvonareva will face the all-Russian duo of Anna Blinkova and Veronika Kudermetova, who shocked No.4 seeds Kveta Peschke of the Czech Republic and Demi Schuurs of the Netherlands, 6-4, 6-2, in just an hour and 13 minutes.

Siegemund and Zvonareva, who beat No.7 seeds Victoria Azarenka and Sofia Kenin in the last round, are pairing up for the very first time this fortnight, but they gave the impression of being a long-time partnership as they combined beautifully to oust the second seeds.

The victors had 25 winners to their opponents' 23, had 11 fewer unforced errors, and won nearly 60 percent of points returning serve.

The shock is muted, as both players have had Grand Slam doubles glory in the past. 2006 US Open women's doubles champion Zvonareva has two women's doubles titles and two mixed doubles titles at Grand Slam level to her credit, while Siegemund was also a mixed doubles champion at the 2016 US Open.

Nevertheless, it was the defending champions who got off to the hot start, as a sturdy service return by the powerful Sabalenka gave her team a break of Siegemund at love for a 3-1 lead. However, the lead was short-lived, as Siegemund and Zvonareva got back on serve in the very next game after Sabalenka misfired long on a backhand on break point.

The German-Russian pairing got on a roll from there, as they earned a second consecutive break, this time on Mertens’ serve, as Siegemund attacked all of her shots in the forecourt. After saving a break point at 4-3, Siegemund and Zvonareva earned a set point at 5-4 with an angled forehand winner by the German. Zvonareva converted it by forcing a long Mertens return, wrapping up the one-set lead.

Siegemund cracked open the second set with a blistering backhand return winner to break Sabalenka in the opening game, and after gritting through a lengthy battle on her serve by saving five break points to hold for 5-3, she and Zvonareva were inches away from the semifinals. The pair held two match points on Sabalenka’s serve in the next game, and victory seemed imminent.

However, Sabalenka got her team out of trouble, holding for 5-4, and she and Mertens suddenly made a late charge by breaking the serve of Zvonareva at love, leveling the set at 5-5. Siegemund and Zvonareva, though, stayed steely, and held on through to the tiebreak. In the breaker, Siegemund and Zvonareva dominated, and they collected the upset over the reigning titlists.

Meanwhile, Blinkova and Kudermetova ended the seven-match winning streak of Peschke and Schuurs, who won last week's Western & Southern Open title at the same site. The all-Russian tandem converted five of their six break points on their way to victory. They also had 22 winners to 15 unforced errors, while Peschke and Schuurs had 19 of each.

Blinkova and Kudermetova, who reached the Western & Southern Open quarterfinals last week, stormed back from a deficit in the first set, as they were behind a break at 3-0. They got on board with a love hold for 3-1, and after that, the Russian duo claimed six of the next seven games to snatch the opening set.

From 2-2 all in the second set, Blinkova and Kudermetova reeled off four straight games, including from 0-40 down in the final game, to seal their spot in the semifinals -- a first trip into the final four of a major doubles event for both of them.

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