Former US Open winner Bianca Andreescu and world number two Aryna Sabalenka cruised into the last-16 of the Miami Open on Sunday with straight sets victories at Hard Rock Stadium.

Sabalenka's power was simply too much for Czech Marie Bouzkova, with the Belarussian breaking serve twice in the opening set on the way to a 6-1, 6-2 victory.

Any chance of a comeback from Bouzkova vanished when she was broken in the opening game of the second set and Sabalenka was in no danger on her serve, not facing break point at any time in the 66 minute encounter.

"There were really great things from me," said an upbeat Sabalenka.

"I felt like everything I was doing was right and I am super happy with the level," she added.

Sabalenka had been hampered by a groin injury in her previous match, receiving medical attention and wincing at moments in her win over Shelby Rogers, but she said the injury, while not resolved, had improved.

"We are working on that. I would say I have the best team and I really trust them and believe that they can fix it. It definitely felt much better," she said.

"My team did everything to make sure that I am not focusing on the leg and I am focusing on the match," she added.

- Player reborn -

Andreescu, who returned last year after a seven month 'mental health break' looks a player reborn and she oozed confidence as she enjoyed a 6-4, 6-4 victory over American Sofia Kenin.

The 22-year-old Andreescu, the 2019 US Open winner, has been impressive so far having beaten Emma Raducanu and world number 10 Maria Sakkari in the previous rounds.

In a match with few rallies, Andreescu dominated with her serve game, with a 70% first serve percentage and it was not until mid-way through the second set that Kenin caused any real problems.

Kenin, the 2020 Australian Open winner, broke Andreescu to cut the lead to 4-3 but despite the improved forehand from the Floridian, Andreescu kept her cool and won with her first match point.

"These victories are definitely very sweet and I've had many tough matches against Sofia, so it feels really good to get through," said Andreescu who converted all three of her break points.

"I definitely feel like I am getting better match by match, even physically. Like I'm feeling really good. I'm feeling very fresh," she added.

Andreescu will face Russian Ekaterina Alexandrova in the next round after she beat world number nine Belinda Bencic of Switzerland 7-6 (10/8), 6-3.

In a good day for Russian women, qualifier Varvara Gracheva reached her second straight WTA 1000 fourth round with a straightforward 6-1, 6-2 win over Polish lucky loser Magdalena Frech.

The 22-year-old Gracheva also made it to the last 16 as a qualifier at Indian Wells.

There will also be a strong Czech presence in the fourth round with Petra Kvitova, Barbara Krejcikova and Marketa Vondrousova all winning on Sunday.

Two-times Wimbledon winner Kvitova beat Donna Vekic 6-4, 7-6 (7/3), surviving a strong effort from the Croat in the second set.

"She was always coming back after a (service) break, and it wasn't really easy already in the first set. ... It was very difficult, she played very well, she served very well," said Kvitova.

Krejcikova, the 2021 French Open winner, beat American Madison Keys 7-6 (7/4), 6-3 and will face Sabalenka next while Vondrousova beat out-of-form compatriot Karolina Pliskova 6-1, 6-2

Romanian Sorana Cirstea made it to the fourth round in Miami for the first time in a decade after beating Czech Karolina Muchova 7-5, 6-1.

The 32-year-old, now coached by Swedish former Australian Open winner Thomas Johansson, is enjoying a mini-revival after also reaching the same stage in Indian Wells this month.