Russian 15-year-old Mirra Andreeva's stunning run at the Madrid Open continued with a 7-6 (8-6) 6-3 win over world number 14 Beatriz Haddad Maia.

Her win over Brazil's Haddad Maia came 24 hours after she beat 2021 US Open finalist Leylah Fernandez in round one.

Elsewhere, American Coco Gauff beat Spain's Irene Burillo Escorihuela.

Gauff, 19, needed only one hour and 17 minutes to clinch a 6-4 6-1 victory and will play Paula Badosa - another Spaniard - in the third round.

Gauff, who also burst on to the WTA Tour as a 15-year-old in 2019, was the last before Andreeva to beat a top-20 player while aged under 16.

Following her impressive back-to-back wins, Andreeva will face Poland's 17th seed Magda Linette - a semi-finalist at the Australian Open in January - in the last 32.

"I'm a bit surprised to be in the third round but also everyone was telling me they are playing the same level as you, they are just more consistent," said 194th-ranked Andreeva.

"Their mental level is different but the game-level is almost the same."

Former world number two Badosa was hampered by a leg injury against Italy's Elisabetta Cocciaretto but dug deep to win 6-3 4-6 6-4 in a match lasting two hours and 30 minutes.

Germany's Jule Niemeier caused an upset as she defeated three-time champion Petra Kvitova, with the Czech 10th seed losing 7-6 (11-9) 6-1.

A Wimbledon quarter-finalist last year, Thursday's win was a second career top-10 victory for 23-year-old Niemeier.