Iga Swiatek was in a ruthless mood as she coasted into the last 16 of the Miami Open, setting up an intriguing clash with Coco Gauff.

Swiatek was in action for the first time since ensuring she will be top of the pile after the next WTA rankings update, and she certainly showed world-number-one form against Madison Brengle in a 6-0 6-3 victory.

The 20-year-old Pole needed just 25 minutes to win the opening set, during which she hit 12 winners to Brengle's one.

Brengle gave a better account of herself in the second set but Swiatek still had far too much for her, with the latter remaining on course to become only the fourth woman to win the so-called 'Sunshine Double' of Indian Wells and the Miami Open.

But certain expectations – particularly those relating to her ranking – are not what Swiatek wants to think about at the moment, especially while she is so content out on the court.

She said: "I know the ranking can be pressure, but on the other hand when I was climbing up and I entered top 10 and top five, I felt the same feeling, and right now I don't want to repeat that. So I just focus on my game.

"I don't know what's going to happen after the tournament and the adrenaline will go down and I have more time to stress about that a little bit more, but for now I feel great. It's not like it's bothering me, it's more motivating me. So it's great."

Gauff, competing in her local tournament, awaits after showing admirable spirit to beat Zhang Shuai 7-6 (7-1) 7-5.

The 18-year-old had to save two set points in the opener before rallying back and producing a devastating display in the tiebreaker.

She then came back from 4-2 down in the second, winning five of the final six games to seal a hard-fought victory.

Another teenager hoping to leave a lasting impression is 16-year-old Linda Fruhvirtova, who became the youngest player to reach the fourth round in Miami since Maria Sharapova and Tatiana Golovin in 2004 – both were also 16.

Fruhvirtova was 6-2 3-0 up over Victoria Azarenka before the three-time Miami Open winner retired, giving the youngster her first top-20 scalp.

Jessica Pegula, Petra Kvitova and Paula Badosa were among the others to secure their progression on Sunday.