After a rain-delayed start, the Russian appeared to be in a hurry to get off court again and won 14 of the first 15 points as she raced into a 4-0 lead before clinching an easy first set.
The battling Australian had no answer to Sharapova's range of shots in the second set and Russian clinched her 23rd career title and first in Rome with another devastating forehand winner.
"I'm so excited to be champion of this tournament, it's something I've dreamed about," Sharapova, who beat world number one Caroline Wozniacki en route to the final, said while clutching the trophy.
"It's been a while since I've won a title. I'm sure I wasn't the favourite so to be the champion and beat players who have had great results on clay means a lot to me. This is just the beginning of many things to come."
Stosur blamed her listless performance on her ailing health.
"I wasn't feeling very well when I woke up this morning," Stosur told reporters.
"Then going down 4-0 is not the start you want against Maria. In the second set I had a few opportunities but unfortunately I wasn't able to take those and the match was over."
Stosur, who had committed 14 unforced errors to Sharapova's five in the first set, began the second set with two more wayward forehands as the seventh-seed broke yet again.
But the Australian, runner-up at Roland Garros last year, got lucky in the very next game to break back as her mishit forehand dropped on the baseline to give her a 2-1 lead.
Sharapova, who needs the French Open title to complete a career Grand Slam, kept her focus to take the next three games against an opponent she had beaten in all seven of their previous meetings.
The Russian negated sixth seed Stosur's wayward power game with some canny placements and finished off a long sixth game with two rasping forehands.
The Australian, who sat through the changeover with her head bowed low, finally managed to hold on to two consecutive service games, but she was powerless to stop Sharapova from lifting a second claycourt title in Europe.
"I was ready from the first point and wanted to be aggressive. I tried to take that start away from her," Sharapova said.
"Moving wise I feel better on clay. I feel better and better and although I may not be the best slider or have the strongest legs there's more than that in tennis and that's why I won."
Despite the defeat, Stosur insisted she was in good shape going into the French Open.
"It's been a great week. Each week here in Europe I've got better and that's what you want heading into a grand slam. I'll take those positives into Paris," she said.
- ReutersTags: sport, tennis, italy First posted May 16, 2011 05:40:00