MELBOURNE (REUTERS) - China's Zhang Shuai became the first women's qualifier since 1990 to reach the Australian Open tennis quarter-finals after beating a hobbling Madison Keys 3-6, 6-3, 6-3 late on Monday night.

The 15th-seeded American had comfortably won the opening set but was broken by the Chinese player in the third game of the second and immediately took a medical time-out for treatment to what appeared to be a left leg injury.

Keys, 20, then found it difficult to move around the court and the 27-year-old Zhang used that to her advantage to make the American chase the ball and send it to a decider.

Keys, a semi-finalist last year, looked on the verge of retiring several times in the deciding set but battled on grimly despite being in obvious pain.

The 133rd-ranked Zhang struggled to control her nerves in the decider, but eventually held it together to set up a quarter-final against unseeded Briton Johanna Konta.

The last qualifier to reach the Australian Open quarter-finals was Mexico's Angelica Gavaldon in 1990.

"I was very lucky today," a smiling Zhang said in an on-court interview after the match which finished around midnight local time.