Garbiñe Muguruza earned her tour-leading 20th match-win of the season in the third round of the Miami Open on Sunday. 

The No.12 seed overcame a stern challenge from Russian wildcard Anna Kalinskaya, ultimately prevailing 4-6, 6-3, 6-4. Muguruza was behind 0-3 in the final set but charged back to win the match in 2 hours and 41 minutes.

"I brought my fighting spirit and I could match the level of fighting against Anna, and very happy to go through these tough matches," Muguruza said in her post-match press conference. "Doesn't matter if you play pretty or you play ugly, but you stay strong and you go through these rounds. That gives me an opportunity to feel better and to have another chance."

Not only does Muguruza have the most match-wins on tour in 2021, but her three final appearances are also the most on the WTA this season. Muguruza finished as runner-up at the Yarra Valley Classic in Melbourne and in Doha before winning her first title of the year in Dubai.

But Muguruza's eighth straight match-win came via a grueling comeback, as World No.115 Kalinskaya pulled the Spaniard into numerous rallies and found some stunning winners to match the former World No.1 for the full duration of the clash.

"It was a very physical match, was a long match and a lot of ups and downs," Muguruza said. "It was tough conditions with wind, so it was a lot about staying strong, staying strong in important moments."

A seven-minute game to open the match set the tone, as Muguruza needed to save three break points just to hold for 1-0. But sturdy hitting from Kalinskaya drew errors from Muguruza and gave the wildcard the only break of the opening set at 3-3, and she would eventually close out the one set lead with a backhand winner.

Muguruza's 3-1 lead in the second set was erased by errors as Kalinskaya clawed back on serve at 4-3. But two-time Grand Slam champion Muguruza broke again for 5-3 after coming out on top in lengthy rallies with backhand winners, and the Spaniard punched a backhand volley to hold at love and level the match at a set apiece.

2021 Miami Highlights: Muguruza battles past Kalinskaya

As the decider started, Kalinskaya took command, controlling points with strong forehands and great depth of shot to ease to an early 3-0 advantage. Muguruza used her experience to strike back with a deft combination of power and placement, and eventually got level at 3-3.

Rallies and games were pushed to the limit and it was Muguruza who broke through first, using a deep backhand return to force an error and claim the break for 5-4. Serving for the match, Muguruza had to save a break point in another extended game, but, on her fourth match point, the former World No.1 fired a forehand winner to wrap up the match.

"At the end I had many match points and I didn't convert them, but they are still match points," Muguruza said. "So I have to stay calm and say, 'Hey, I might not have won but I'm still 5-4 serving, right? So why should I be sad? I will try to get the next opportunity.' These are the key moments, and with experience you learn a little bit more how to handle them."

No.16 seed Elise Mertens also needed to pull through a three-setter to move into the round of 16 on Sunday. The Belgian survived a topsy-turvy match against No.22 seed Anett Kontaveit, winning 6-2, 0-6, 6-2.

Mertens has now won at least two consecutive matches for an 11th straight tournament, but it required shaking off a rough second set before outlasting Kontaveit in an hour and 47 minutes.

"It just didn't work out in the second set," Mertens said in her post-match press conference. "I just tried to refresh.

"There is another set that has to be played, and I just tried to give much more energy. I also tried to put more balls in the court in general because that was kind of necessary.

"But I think mentally I was prepared for a battle, even though it was maybe not my best day. But it's kind of the little change that I made during the third set that got me the win, and that's how I'm going to look at it positively."

Mertens cruised through the first set, breaking Kontaveit three times in succession to start the match, wrapping up the opening frame with an ace.

However, Kontaveit toppled Mertens in the second set as she grabbed the bagel on her fifth set point. Mertens and Kontaveit each had six winners in the second set, but Kontaveit’s five unforced errors during that timeframe was wildly exceeded by Mertens’ 17.

But as quickly as the momentum switched to Kontaveit, it switched right back to Mertens in the final set. Mertens notched two easy service breaks in a row to lead 4-1, then used incredible all-court play to put together a stellar final game and close out a routine decider.

It was a breakthrough win at the event for Mertens, who had been stopped in the third round in her two previous Miami main-draw appearances. In her first-ever fourth-round match in Miami, Mertens will face No.2 seed Naomi Osaka.