It completed a miserable evening for the five-times grand slam champion, currently ranked 211, who earlier found out that she had been refused a wildcard for the French Open.
The French Tennis Federation decided against awarding the former world number one even a place in the qualifying event -- a move that surprised many.
Sharapova had needed to reach the semi-finals in Rome to avoid needing a wildcard for the Wimbledon main draw.
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However, her first round win against American Christina McHale in Rome means that her ranking will rise back inside the world's top 200 just in time to be guaranteed a place in the Wimbledon qualifying tournament.
A decision as to whether she is granted a main draw spot will be taken on June 20.
Sharapova, banned after testing positive for heart drug meldonium at the 2016 Australian Open, has had mixed results since re-joining the WTA Tour.
She reached the semi-finals as a wildcard in Stuttgart but fell early in Madrid to Eugenie Bouchard who days earlier had labelled the Russian a "cheater".
Sharapova, also awarded a wildcard in Rome, dropped the first set 6-4 against veteran Lucic-Baroni but battled back to take the second 6-3.
She appeared to be struggling though and stopped early in the third set. She did not hold the usual post-match news conference but issued a statement.
"I apologise for having to withdraw from my match with a left thigh injury," she said.
"I will be getting all the necessary examinations to make sure it's not serious. I want to thank the organisers for giving me the opportunity to play in this special event again."
Lucic-Baroni will face a possible meeting with world number one Angelique Kerber in the next round if she beats Anett Kontaveit.
(Reporting by Martyn Herman; Editing by Toby Davis)
