It was a tour-best fourth title this year for Svitolina and the most prestigious trophy of her career so far. The 22-year-old Ukrainian also leads the tour with 31 match wins this season, putting her among the favorites for the French Open, which starts next Sunday.
"Every day I'm just trying to work on my mental part, my physical, my tennis," Svitolina said. "Everything just came together and I'm very happy that it's happened in such a big tournament."
The fourth-ranked Halep was in full control and serving for the first set at 5-2 when she rolled her right ankle while sliding over what appeared to be a small hole in the Foro Italico stadium court.
While Halep was able to eventually win the opening set, she required treatment to her ankle from a trainer twice and was late getting to shots as the match wore on.
"Sorry guys for third set," Halep told the crowd. "It was a little tough for me to get through but Elina played great."
Halep was playing in her second clay-court final in two weeks after winning the title in Madrid last Sunday.
Svitolina also required medical treatment from a trainer midway through the second set, for an apparent problem with her left leg.
"Hopefully we'll recover, me and Simona, because we're struggling a bit physically," Svitolina said.
During the post-match presentation, Svitolina dropped the cover of the silver trophy on to the red clay court, prompting her to say, "Oops."
The first two sets featured long, nervous baseline rallies in which both players waited for their opponent to commit errors.
"It was very tough first two sets and I'm really happy that it's all finished," Svitolina said.
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