Australian Open semi-finalist Madison Keys was bundled out of the Abierto Akron Zapopan in Guadalajara on Monday after a shock three-set loss to Harmony Tan.

Frenchwoman Tan, who is ranked outside the top 100, toppled the second seed in one hour and 46 minutes, winning 6-4 1-6 6-1.

In a seesawing battle, Tan's shotmaking and deft touch was a highlight, helping her steady after emphatically dropping the second set, before winning the first five games of the final set.

The win was Tan's first-ever victory against a top 30 player, qualifying her for the second round where she will play China's Wang Qiang who won 6-2 6-1 over Lauren Davis.

American sixth seed Sloane Stephens did not have such problems in her first-round encounter with qualifier Brenda Fruhvirtova, triumphing 6-2 6-2.

The 14-year-old Czech had enjoyed a good qualifying run but was thwarted by the 2017 US Open champion in 58 minutes.

Fruhvirtova had become the youngest player to compete in a WTA Tour main draw match since Keys in April 2009 at Ponte Vedra Beach.

Fifth seed Nuria Parrizas Diaz bowed out 6-1 6-4 to Slovakia's Ana Karolina Schmiedlova in one hour and 10 minutes. Schmiedlova will face Anastasia Potapova who progressed 6-4 2-2 after Lesia Tsurenko retired.

Japanese seventh seed Misaki Doi also exited, going down 4-6 7-5 6-4 to Marie Bouzkova in the late match, setting up a second-round date with qualifier Lucia Bronzetti who edged American wildcard Caty McNally 6-7 (5-7) 6-3 6-3.

Zheng Qinwen was another seeded casualty, with the Chinese eighth seed going down 6-3 2-6 6-2 to Anna Kalinskaya.