San Francisco Frontiers - Rybakina, Sabalenka march on in Miami, Pegula progresses

But there was agony for Canadian former US Open winner Bianca Andreescu, who had to be wheelchaired off court after suffering a left ankle injury and retiring against Ekaterina Alexandrova.

Rybakina is looking to complete the "Sunshine Double" after her triumph in Indian Wells, but she was far from euphoric after her victory.

"Physically I'm not the freshest, but I'm happy that I'm managing and finding my way. To be in a quarter-final is great and hopefully I'm going to play better," she said.

The Kazakh allowed Mertens to break in the sixth game of the first set but then two double faults from the Belgian allowed Rybakina to swiftly break back and then she struck again to take the opening set.

The Wimbledon champion broke early in the second set and never looked back and she will now face Italian Martina Trevisan in the quarters.

Trevisan beat former French Open winner Jelena Ostapenko 6-3, 6-3.

Sabalenka looked in ominous form as she blasted her way to victory over Krejcikova, the 2021 French Open winner, 6-3, 6-2.

Krejcikova had ended Sabalenka's 13-match win streak in February in Dubai but Sabalenka defeated the Czech two weeks ago at Indian Wells.

This time Sabalenka took just 65 minutes to take care of business, going unbroken in the match and facing just one break point.

The Belarusian lost just 10 points on her serve and will start as strong favourite on Wednesday against Romanian Sorana Cristea.

Andreescu's return to form was cut brutally short when she suffered a left ankle injury in her match against Ekaterina Alexandrova.

While attempting a return, Andreescu injured the ankle, collapsing to the court as she yelled in pain.

After receiving medical attention on court she was lifted into a wheelchair and taken off court in tears.

The 22-year-old, who won the US Open in 2019 but then missed all of 2020 due to injury, returned to the circuit last April after a six-month break.

In Miami she has looked very much back to her best with wins over Emma Raducanu, Maria Sakkari and Sofia Kenin.

American Jessica Pegula looked comfortable and in command of her game as she beat Poland's Magda Linette 6-1, 7-5.

World number three Pegula got off to a flying start - she struck seven winners in the opening nine minutes and won the first three games. With only 19 minutes on the clock she was 5-0 up.

The second set was a different story though with Linette grabbing a 5-2 lead. However, she twice let set point slip on her serve and Pegula went on to win the final five games to secure victory.

- Weird match -

Pegula had lamented her slow starts at Indian Wells but said her rapid-fire opening to matches in Miami had not been part of any strategy.

"It wasn't something I was really thinking about. I think it just has been happening that way, which is nice," she said.

"It was kind of a weird match. I had strings of games where I was playing really well, then (went) a little bit off. For the most part I was able string together good games, so that's always a good sign," she said.

The American will face Anastasia Potapova after the Russian beat China's Zheng Qinwen 6-4, 7-6 (7/4) to continue her impressive run.

Romanian Cirstea followed up her quarter-final at Indian Wells by securing another last eight appearance thanks to a 7-6 (7-3), 6-4, win over Czech Marketa Vondrousova.

Revitalised by her Swedish coach Thomas Johansson, Cirstea is enjoying a revival in fortunes at the age of 32 but knows she will need to produce one of the performances of her life is she is to get past Sabalenka.

"I know it's going to be very tough but I've been winning a lot of matches this American swing and I have the confidence. I know what I can play."

Z.Sanchez--SFF