"These are very tricky rounds where in a big tournament with a big draw that you face players that some of them are unknown," Muguruza said in press.
"Doesn't mean they don't have a great level, and today was proof of that. I felt I didn't brought my best tennis on court, but I brought my fighting spirit and I could match the level of fighting against Anna, and very happy to go through these tough matches. Doesn't matter if you play pretty or ugly, but you stay strong and you go through these rounds. That gives me an opportunity to feel better and to have another chance."
Fresh off a first title of 2021 at the Dubai Duty Free Tennis Championships, Muguruza is playing far better than her No. 12 seed would suggest, and unleashed that form when she needed it most to close out the Russian wild card in two hours and 41 minutes on Butch Buchholz court.
Muguruza made her maiden WTA main draw appearance as a wild card in Miami back in 2012, and scored back-to-back wins over Vera Zvonareva and Flavia Pennetta en route to the fourth round. Despite that promising debut, the Spaniard has often struggled in the Sunshine State, never making it past the round of 16 in eight subsequent attempts.
Kalinskaya saved three match points before bowing out to Muguruza in Miami. (Getty Images)
"This is totally my breakthrough tournament almost 10 years ago when they gave me a wildcard," Muguruza recalled. "I actually played well. I beat two top 10 players, and that was a great sign for me that I had the level and I just had to learn many more things and become a better player."
Meanwhile, the 22-year-old Kalinskaya was making the most of her own wild card this week at the Hard Rock Stadium, knocking out No. 20 seed Petra Martic in a third-set tie-break to book the clash with Muguruza for only her sixth career match against a Top 20 player.
Coached by former WTA pro Patricia Tarabini, Kalinskaya scored the only break of the first and shook off a second set dip to lead 3-0 in the decider, seemingly giving herself the momentum necessary for the biggest win of her career.
Buoyed by her on-fire start to the season and continued success with coach Conchita Martinez, Muguruza dealt with the sweltering heat and reeled off six of the final seven games—surviving a titanic final game in which Kalinskaya saved three match points in scintillating fashion before the Spaniard ultimately secured victory.
Standing between the two-time Grand Slam champion and a first-ever Miami Open quarterfinal will be either 2019 US Open champion Bianca Andreescu or Amanda Anisimova, who reached the Roland Garros semifinals that same year.
"I feel excited whoever wins. I don't have a preference. I have played both, so that gives me an idea of what to expect. There is no easy matches today. I had very tough matches and I expect every time the same level of game, because this is really, since I started this year, every match is hard."
Andreescu and Anisimova last played as juniors at the Eddie Herr International Tennis Championships in 2015, and will face off in Sunday’s evening session.
Earlier in the day, American Jessica Pegula pulled off an improbable third straight win against former world No. 1 Karolina Pliskova, 6-1, 4-6, 6-4. After sweeping their Middle East series in Doha and Dubai, Pegula looked at last out of ideas as Pliskova reversed a 6-1, 4-1 deficit to find herself ahead 4-2 in the third.
"It was definitely a different feeling, beating her this time," Pegula said after the match. "It was tougher. She played better. Maybe I was not expected to win but I beat her the last two times. It's, like, 'Okay, can you do it again?'"
A quarterfinalist at this year’s Australian Open, Pegula would not be denied and won the last four games of the match to continue her breakthrough season.
Pegula previously beat Pliskova at both Middle East events in Doha and Dubai ahead of their Miami meeting. (Getty Images)
"I definitely knew what to expect. I kind of expected her to play well there. Even when I was up I still felt like she could easily come back just because she plays so aggressive and she serves well.
"So I knew it could switch at any second, and it did. She played really well, and maybe I got a little passive, but I think mentally it was more mental today in that third set to come back and to break, hold and break was pretty big."
Up next for the No. 29 seed is No. 23 seed Maria Sakkari, who easily dispatched Russian qualifier Liudmilla Samsonova, 6-0, 6-1. Sakkari last played Pegula on grass back in 2019, dropping just three games at the Nature Valley International in Eastbourne.
"I'm playing much better now," Pegula said. "I know she's been playing pretty well and kind of solidified her as a really good top player, dangerous, amazing athlete. I know she's a warrior, she's gonna battle, not give it away. Just going to be another tough match tomorrow. Yeah, I'll be ready for it."
No. 16 seed Elise Mertens booked a marquee fourth-round encounter with reigning US and Australian Open champion Naomi Osaka, who advanced when Serbian qualifier Nina Stojanovic withdrew with a right thigh injury, after avoiding an upset against No. 22 seed Anett Kontaveit. Kontaveit managed an emphatic 6-0 second set but couldn’t keep it up against the Belgian, bowing out, 6-2, 0-6, 6-2.