Veronika Kudermetova continued her torrid run on the clay this season with a 6-4, 6-3 upset of defending champion Kiki Bertens in the second round of the Mutua Madrid Open.

"I think it was a really tough match because she’s a good player, every time she’s fighting," Kudermetova said on court, after her victory. "I’m really happy about my win today."

Kudermetova, currently ranked at a career-high World No.28, has gone 11-1 since the tour hit the dirt, winning her first career WTA singles title at the Volvo Car Open in Charleston, then following up with a semifinal run last week in Istanbul.

Her hot streak continued on Saturday with her 80-minute victory over World No.10 Bertens, accounting for the sixth Top 10 victory of her career. Kudermetova fired 23 winners and converted four of her six break points on the day.

Bertens, who claimed the Madrid title at the event's most recent edition in 2019, was up an early break in each set, but the Dutchwoman eventually was undone by 18 unforced errors, five more than her winner total of 13.

READ MORE: Champions Corner: Inside Kudermetova's perfect week in Charleston

Bertens's 4-2 lead in the opening set was erased by sturdy returning from Kudermetova two games later, as she converted her third break point of that game to level the set at 4-4 after an errant dropshot by the seeded player.

Kudermetova continued to stay aggressive, including saving a break point at 4-4 by ending a scintillating rally with a passing winner. She was rewarded with four straight games to end the opener, capping off the set with one final break of service.

Kudermetova upsets defending champ Bertens: Madrid Highlights

2021 Madrid

Another four-game winning streak helped Kudermetova storm back from the early break down in the second set as well, as the Russian found angles and the lines to punctuate points.

A love service hold for 5-3 helped Bertens stop that streak, but Kudermetova coolly served out the match with a serve-forehand combo on her first match point.

Kudermetova will now face another former Madrid champion in the round of 16: a three-time champion, to boot, in the form of No.9 seed Petra Kvitova. Kvitova ousted Angelique Kerber in straight sets earlier on Saturday to claim her round-of-16 spot.

"I’ve never played against [Kvitova]," Kudermetova said. "She’s a great player, she’s a Grand Slam champion, and I’m really looking forward to the next round."

Meanwhile, No.8 seed Belinda Bencic survived an upset bid, as she eked out a 3-6, 6-1, 7-6(5) victory over American qualifier Bernarda Pera which ended after midnight.

Two hours and 39 minutes of back-and-forth tennis finally went the way of the World No.11 as she held off the challenge from the hard-hitting left-hander ranked 70th in the world.

It was an important win for Bencic, who was a semifinalist at the most recent edition of the Mutua Madrid Open in 2019. The Swiss player picked up back-to-back victories for the first time since her run to the Adelaide final in early February. 

The constant aggression from Pera notched her 43 winners in the nightcap, outpacing Bencic's 25 winners, and she was a whisker away from her third career win over a Top 20 player before Bencic edged out the final-set tiebreak.

An opening set with five breaks of service went the way of Pera, who perpetually was on the attack on return and used that shot to great effect. Pera fired 17 winners to just five unforced errors in the first set. But Bencic rebounded swiftly in the second set, reeling off the first five games to level the match with ease.

An engrossing final set followed, where Bencic had seven break points and multiple opportunities to take charge, but hard-hitting Pera swatted those away with aplomb in a set with zero service breaks.

Naturally, the duo settled affairs in a decisive tiebreak. The pair stayed level up to 5-5, when Bencic earned a match point with a winning rally forehand. Unfortunately for Pera, at that moment, she picked the worst possible time to hit her fifth double fault, ending the barnburner and sending Bencic into a round-of-16 meeting with Ons Jabeur.

The remaining night match went to a homeland hope, as Spain's Paula Badosa overcame Jil Teichmann of Switzerland, 5-7, 6-1, 6-2 in a hair over two hours.

Badosa, the only one of the five main-draw wildcards to win her opening-round match, continues her best-ever run in the Spanish capital. She fell in the first round in her two previous main-draw appearances, in 2015 and 2016.

"It means a lot," Badosa told the press, after her win. "I love this tournament. It's my favorite tournament. I love to play on clay. I'm feeling very good since Charleston. I'm having very good feelings on the clay court."

Overall, Teichmann had three more winners than Badosa but 15 more unforced errors, as the Spaniard was sturdier down the stretch to execute the comeback and set up a round-of-16 clash with Anastasija Sevastova.

"At the beginning of the first set, I wasn't feeling myself," Badosa said. "I was missing a little bit, quite too much. But then I started to hit very hard, aggressive. I knew in the match the key was to hit hard because she's a player that moves you a lot, very talented, very creative.

"I knew I had to hit the first two, three balls very hard. That's what I started to do. I started to find myself. That was the key."