The fourth seed from Romania was serving at 4-4 in the deciding set when umpire Kader Nouni awarded the first point to Sharapova after overruling a linesperson.
The Russian had hit a shot that was called out, but only after Halep had failed to return the ball back into court.
Halep felt the point should be replayed as she had made contact with the ball, but the umpire disagreed.
"I thought that we have to replay the point because I touched the ball," Halep explained.
"But the rule is, no, if I don't put the ball on the court we cannot replay the point. So I think that ball was very important at that moment."
Sharapova moved 15-0 up and went for the throat as Halep struggled to keep her emotions in check. She won the game to love and served for the match, winning 6-4 6-7(5) 6-4.
"I couldn't manage my nerves maybe and I couldn't stay very focused for the next points," the 22-year-old Halep admitted.
"That's it. That's life."
Sharapova won her fifth grand slam title and her second at Roland Garros.
Halep, however, showed she can be a force in the future, having reached her first grand slam final after making the last eight at the Australian Open earlier this year.
"(I learnt that) I can play at a very high level," she said.
"I saw that I can play well in grand slams, because before (at other majors) I had pressure.
"Before the tournament, in grand slams I could not play my best tennis. But here I did, and I'm really proud of this."
She showed her mettle in the second set tiebreak when Sharapova moved 5-3 up and two points from victory.
When Halep won the next point she started to believe that anything was possible.
"At 5-4, I had a feeling that I can win the set. It was really tough at that moment," Halep, who had not lost a set before the final, said.
"I believed in my chance to win the second set and to try to win the match in third set. I did very well. I tried everything at that moment and it worked for me."
In the end, however, Sharapova was too strong and the experience she had gained from her previous eight grand slam finals prevailed.
"She is very strong mentally. She's a strong person. And also in important moments she's hitting very strong," said Halep, who last season won six titles to be named the WTA's most improved player.
Halep has clearly improved this year as well and on Monday will move up one place to number three in the rankings.