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.
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)
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