A Wednesday chock full of upsets at the bett1open ended with the biggest one yet, as Madison Keys of the United States knocked out No.1 seed Aryna Sabalenka of Belarus, 6-4, 1-6, 7-5.

Keys upended Sabalenka in just under two hours, as the American made it into the quarterfinals of a WTA event for the first time since January of 2020, when she finished as the runner-up in Brisbane.

Read more: Cornet edges Andreescu, Alexandrova serves past Svitolina in Berlin upsets

The American collected her eighth career win over a Top 5 opponent by outlasting World No.4 Sabalenka. Keys had 31 winners to just 17 unforced errors in the clash, and saved 10 of the 14 break points she faced to eke out the win.

Former World No.7 Keys, currently ranked 28th, is eyeing a third WTA singles title on grass this week as she attempts to rise back up the rankings. Two of Keys's five career titles have come on the surface: 2014 Eastbourne and 2016 Birmingham.

Keys’s power game was in full effect in the opening stages of the clash as she zipped to a 4-0 lead. Sabalenka eventually got her feet under her and steered the set back to 4-3, but Keys stopped that streak by holding for 5-3 with a backhand winner down the line. Then, at 5-4, 30-30, Keys slammed two consecutive superb serves to grit out a close hold and claim the opening set.

The second set, however, went all Sabalenka’s way. From 1-1, Sabalenka reeled off five straight games as Keys twice dropped serve with double faults on break point, at 2-1 and 4-1. Sabalenka had to save three break points while serving for the set at 5-1, but the top seed prevailed in that game with well-timed service winners, including one on her third set point.

Sabalenka extended her momentum at the outset of the final set as she broke Keys in the opening game, but the American got back on track, firing a forehand passing winner to break back for 2-2. Each player saved one additional break point mid-set as they used strong serves and deft net play to maintain level footing through 5-5.

Stupendous serving helped Keys nudge ahead with a hold for 6-5, and after that, the American took her chance. A nimble dropshot winner brought Keys to 30-30 in that game, and Sabalenka followed that point with a netted miscue to set up Keys’s first match point. There, Sabalenka hit a forehand long, and Keys attained the crucial break to close out an upset win.

Keys will face a Russian in the quarterfinals: either Veronika Kudermetova or qualifier Liudmila Samsonova, who will meet in their second-round clash on Thursday.

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2021 Berlin

Belinda Bencic was the only seeded player to survive on Wednesday in Berlin. The No.5 seed from Switzerland defeated Petra Martic of Croatia, 6-3, 6-4, in an hour and 23 minutes.

12th-ranked Bencic moved into her third quarterfinal of the season as she ousted World No.25 Martic in two close sets, winning 83 percent of her first-service points. Bencic successfully fended off each and every one of the five break points she faced on the day.

Bencic, who has one grass-court title on her resume (defeating Agnieszka Radwanska in the 2015 Eastbourne final), collected the critical service break in the first set at 3-2, which she claimed with a winning passing shot. Bencic coolly moved through the remainder of the set, taking the one-set lead with a forehand crosscourt winner on her first set point.

The second set was at a stalemate until 4-4, where Bencic won one of the best points of the season to break for a 5-4 lead. After chasing down a dropshot, Bencic fell on a smash, but stayed alive with a focused volley while still on the ground, then stood up to put away a backhand winner, raising her arms in triumph.

Bencic eased to victory from there, finishing the match in the next game with a backhand winner. The Swiss player will next meet Russia's Ekaterina Alexandrova, who upset No.2 seed Elina Svitolina, in the quarterfinals.