Miami, March 27 (IANS): Women's World No.2 Maria Sharapova has been beaten by 97th-ranked Russian Daria Gavrilova 6-7 (4), 3-6 at the Miami Open tennis tournament's second round.

The early exit for the five-time Grand Slam winner on Thursday is the biggest upset so far at the Masters tennis tournament, reports Xinhua.

Sharapova lost in the first round here on her tournament debut in 2003. Thursday's defeat is her opening match in Miami after took a first round bye.

"Of course it's a bit of a surprise. I'm expected to win," said the Russian, who has never lifted the trophy in Miami despite five trips to the final.

It was also a surprise for Gavrilova.

"I still can't realise that it's my dream," said Gavrilova, who said she had dreamed of beating Sharapova ever since she saw her compatriot beat No.1 Serena Williams in the Wimbledon final in 2004.

Sharapova lost the opening set after nearly an hour and quickly found herself trailing the former junior No.1 1-4 in the second.

Sharapova clawed a break back but was then broken to love as Gavrilova set herself up for the win with a 5-3 lead and closed out her biggest career win on first match point.

The triumph was Gavrilova's first against a top-10 player. She had never before beaten anyone ranked higher than 35th.

In the men's competition, former US Open champion Argentine Juan Martin Del Potro was beaten by Canadian Vasek Pospisil 4-6, 6-7 (7) in the first round.

The Argentine, who had come back from right wrist surgery in 2010, underwent surgery on his left wrist in March last year.

He finished the 2014 season outside the top 100 for the first time since 2005 after contesting just four tournaments during the year.