The unseeded Spaniard served for the match in the second set, but soon trailed by a break in the third before righting the ship in stellar fashion to win in just under two and a half hours on Center Court.
"I'm very motivated to play top players," she explained after the match. "Like everybody, I've been working hard and fighting for trophies, and to play well in big tournaments. Today, I was facing a top player and I knew I'd have to go out there with a big fighting spirit and feeling strong enough to win against such a tough opponent."
Muguruza arrived in the Middle East after an Aussie swing that showed plenty of promise as she finished runner-up at the Yarra Valley Classic and played what was arguably the match of the Australian Open against eventual champion Naomi Osaka.
"It gives you confidence to play top players and get the win with that fighting spirit. At the same time, I don't see all of the negatives from losses, because just having chances means you're playing well. The level was there, even if a few points here and there mean you don't end up winning. I felt like I'm not far, and that my game is pretty good. I just have to keep showing it every day and stay close to my opponent, even on days when I'm not feeling great, because the opportunities will come."
Despite taking the court without coach Conchita Martinez, who is hotel-bound after testing positive for COVID-19, the Spaniard has channeled disappointment into success in Doha, sweeping aside rising Russian Veronika Kudermetova and enjoyed a strong start against rival Sabalenka in the second round.
Looking to avenge a 2018 China Open defeat to the Belarusian, Muguruza played pitch-perfect tennis on the most important points, and won all of the close games in the opening set to serve it out after saving two break points.
Sabalenka, who rode a 15-match winning streak from the end of 2020 into the start of 2021, took a similarly narrow loss to Serena Williams in Melbourne and won the women’s doubles title alongside Elise Mertens. With a bye through the first round, the world No. 8 dialed in after falling behind by an early break in the second set, winning five of the next six games to thrice edge within two points of a final set.
Again, Muguruza proved more clutch in those crucial moments, reversing the deficit to find herself serving for the match.
The No. 3-seeded Sabalenka put on a brave last stand from there, breaking on her third opportunity and quickly earned the first mini-break of the ensuing tie-break. Muguruza broke back with a searing backhand pass, but Sabalenka overpowered the former world No. 1 with a backhand of her own to level the contest at one set apiece.
"It was a challenge, and a tough set where I had my opportunities and didn't convert them. It's easy to get upset and distracted, and lose, so that was the challenge for me. I needed to stay in the match, start over, and play the final set. I knew that if I didn't match her spirit and level, I was already in the locker room."
With both women playing their best early in the decider, it was Sabalenka who was first with the initiative, emerging from a trilogy of titanic games to break Muguruza with another thunderous backhand.
Muguruza, however, would not be denied, drawing the 22-year-old into one last epic—this time lasting six deuces—to completely reclaim the momentum, losing just two points in the final three games to reach her second quarterfinal of the season.
"It meant a lot of break towards the end of the match. It gives you that extra advantage that you need to close it out. It was such an important game, but I was able to play well and aggressively. I took my opportunities."
Awaiting her there is Greek No. 1 Maria Sakkari, who defeated the two-time major champion at the Abu Dhabi WTA Women's Tennis Open back in January.
"It's tough, no? All of the players are doing so well right now, and they're all so tough. I'll have to be ready for tomorrow. Of course, today was a big battle, but tennis is like that: tomorrow is another day, and it's another match. I'll have another tough opponent, but right now is about recovery and switching my mind towards the next match."
Earlier in the day, doubles partners Victoria Azarenka and Elina Svitolina booked a quarterfinal clash against one another after scoring straight-set victories over Laura Siegemund and Misaki Doi, respectively. Former Doha champion and No. 4 seed Petra Kvitova also eased into the last eight with a 6-1, 6-3 win against Anastasia Pavlyuchenkova.