Rome, Metropolitan City of Rome, Italy, 16 May 2018 | AAP

Australian No.1 Ashleigh Barty has been knocked out in the first round of the Internazionali BNL d’Italia by three-time champion Maria Sharapova.

Making her debut in the main draw in Rome, the 16th-seeded Barty produced a battling performance to take the five-time Grand Slam champion to a deciding set but eventually came off second best, 7-5 3-6 6-2.

Australian qualifier Ajla Tomljanovic went down 6-0 6-4 to Russian 14th seed Daria Kasatkina.

Daria Gavrilova is the last Australian player left in the singles draws in Rome and she takes on third seed Garbone Muguruza on Wednesday.

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Sharapova, who has been struggling to find her form after first-round exits in Stuttgart and Indian Wells and a year on from her return to the court after a doping violation ban last April, needed two hours and 32 minutes to eliminate her battling opponent.

“She made me hit a lot of balls, and that’s the reason why she’s doing so well, seeded here and had the results that she has,” Sharapova said.

Sharapova made a confident start against Barty with an early break but was still prone to mistakes when switching from her backhand to the forehand side.

Her 22-year-old opponent broke serve to pull level at 5-5 in the very first meeting between the two players.

A vicious forehand winner on the line and a Barty net error secured the first set in 50 minutes for Sharapova.

The Russian looked shaky in the second set as a handful of unforced errors saw Barty break her serve twice as the world No.18 levelled the match with a solid service game to force a deciding set.

Sharapova, ranked No.40, then saved three break points to remain even with Barty at 1-1 in the final set before a remarkable lob that caught the baseline gave her the lift she needed to finally get a vital break.

Her revival at the crucial moment drew a nervous double fault and a set of forced errors from Barty when she traded in a rally to concede defeat to the former world No.1.

She now meets Slovakia’s Dominika Cibulkova in the next round, who defeated Italy’s Francesca Schiavone.