The 26-year-old Halep seemed to get better and better as the match progressed and after dropping the opening set, went on to win the final against the 25-year-old Stephens 3-6, 6-4, 6-1 in just over two hours for her first Paris title.
Showing remarkable nerves given that this was only her second Grand Slam final appearance, Stephens consistently held her serve to take the first set 6-3.
"I said there is a chance to come back and win it".
Simona Halep has been undoubtedly one of the world's best players since first reaching the French Open final four years ago, but the world No. 1 could equal the unwanted Open-era record of most Grand Slam finals without a title.
A true class act both on and off the tennis court, Stephens had only good things to say and words of congratulations for Halep following their hard-fought match. Honestly, I could not believe. Halep then fell to 0-3 with a trophy on the line at the Australian Open in January, beaten by Caroline Wozniacki. Stephens won the sixth game before Halep held her serve and completed the victory in front of a delighted Parisien crowd.
"Thanks guys it was wonderful and I felt your support", Halep, twice a runner-up in Paris before today, told the crowd who were chanting her name. "I don't get too up, too down", said Stephens.
Simona Halep didn't need a major to validate her No. 1 ranking.
Upon receiving the trophy she added: "Last year was very emotional so I was living for this moment since I was 14 so thank you and I wanted this moment to happen here in France". She's a great player, always tough to play.
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"It's great that 40 years after Virginia I managed to win".
As Halep scurried to chase a shot that turned into a drop shot for Stephens and won the point for 4-0, her coach Darren Cahill leaped out of his chair and pumped his fist.
The fans at Roland Garros preceded the match with a standing ovation for seven-time Grand Slam champion Maria Bueno after the Brazilian's death on Friday aged 78. - Madison Keys, who lost to Stephens in the semifinals on Thursday. His final season came just months after Sloane was born.
Having worked her way into a strong position in the point Halep netted a straightforward backhand and let her off the hook. He is 10-0 in championship matches at Roland-Garros. "So to be here from there, I think, is rewarding, because those times were not easy".
Halep, down a set and a break, then made Stephens uncomfortable and proved why she's the best in the world right now.
"So I lost three times until now and no one died, so it will be okay", said the Romanian, who leads Stephens 5-2 in their career head-to-head meetings and has won their last four matches in straight sets.
Halep in stride had Stephens grasping.
With their Davis Cup captain Yannick Noah watching from the stands, Herbert and Mahut claimed their third Grand Slam title together by defeating Oliver Marach and Mate Pavic 6-2, 7-6 (4) in the final.