World number two Naomi Osaka and defending champion Ash Barty advanced to the quarter-finals of the Miami Open.

Osaka reached the last eight at the WTA Premier event for the first time in her career thanks to Monday's straight-sets win over Elise Mertens.

World number one Barty overcame two-time grand slam champion Victoria Azarenka in a tough three-set battle in Miami.

THERE'S NO STOPPING OSAKA

Australian Open champion Osaka extended her winning streak to a remarkable 23 matches.

Osaka defeated 16th seed Mertens 6-3 6-3 to stay hot – Venus Williams, Serena Williams, Justine Henin and Azarenka are the only other players with winning streaks of 23 or more matches since 2000.

"It definitely feels very special," four-time major winner Osaka said. "This is one of my favourite tournaments to play, and of course I'm sad I hadn't been able to get to the second week the last times that I have played this tournament. But I'm here now, and hopefully it will go well this time."

Maria Sakkari is next for Osaka after the 23rd seed saved six match points in her 6-4 2-6 7-6 (8-6) win over Jessica Pegula.

BARTY WINS BATTLE OF PAST AND PRESENT NUMBER ONES

In a rollercoaster battle, top seed Barty prevailed 6-1 1-6 6-2 against 14th seed Azarenka.

Barty extended her winning streak in Miami to nine matches after coming out on top against the former world number one.

"Playing against Vika you have to be ready right from the first point," Barty said. "I felt like I did that well in the first set and she gave me a few cheap errors. Then through the second she lifted her intensity.

"I probably wasn't sharp enough in those first couple of games to be able to go with her, particularly with new balls. When Vika is ahead and she's a front runner, she's the very best in the world."

Aryna Sabalenka stands in the way of Barty and the semi-finals after the seventh seed trounced Marketa Vondrousova 6-1 6-2.

SVITOLINA WINS THRILLER, ANDREESCU RALLIES

Fifth seed Elina Svitolina rallied past two-time Wimbledon winner Petra Kvitova 2-6 7-5 7-5.

Svitolina made a slow start against the red-hot ninth seed, but the 2018 WTA Finals champion finished strongly to progress.

Anastasija Sevastova took down Ana Konjuh 6-1 7-5 to set up a clash with Svitolina.

Meanwhile, eighth seed and 2019 US Open champion Bianca Andreescu came from behind to defeat two-time slam winner Garbine Muguruza 3-6 6-3 6-2.