By Julien Pretot
Li, the sixth seed, beat last year's champion Francesca Schiavone of Italy 6-4 7-6 in the final.
Even her sponsor had not been not ultra-confident that Li, who confessed earlier in the tournament that she disliked clay, could win in Paris.
"(My sponsor) made a T-shirt with Chinese characters meaning 'Be Yourself'. They asked me: 'Are you okay to wear it?' I said: 'Yes of course'," Li told a news conference.
"But they only made 30 of them. I think they should make more now because a lot of fans are asking where they can find them."
True to herself, Li dominated a one-sided final as Schiavone was thrown off balance.
"I did not have the feeling I could lose the match," Li said.
Her flat baseline strokes and accurate serve allowed her to dictate the points, with Schiavone scurrying around the red dirt arena on a sunkissed Court Philippe Chatrier.
Fifteen million television viewers, with a peak at 25 million, watched Li qualify for the final as she deflated hard hitter Maria Sharapova in the semi-finals.
Many millions stayed up late into the night in China to watch their 'Golden Flower' bloom into glory Saturday, and Li's win was hailed as a miracle.
"It's a miracle, a breakthrough, a first in more than 100 years of tennis," a breathless presenter on state television's main sports channel exclaimed as Li hit the winning shot.
"I believe tennis in China will grow bigger and bigger," Li said.
However, the Italian's fingers were ripped from the trophy in emphatic style as Li raced through the tiebreak without dropping a point.
"I was up 4-2 and she tried to come back and I thought: 'Okay you've got to stand up', and I made it," Li, who fell backwards to the clay and put her hands to her face in celebration, said at courtside. "I was nervous but I did not want to show it, I was cheating a little bit."
"It's really tough, but I have to say congratulations to Li Na because she improved this year and she played really well today," the 30-year-old Milanese said.
Right from the start Schiavone knew she was in for a scrap as Li, showing great composure, threatened to break in the opening game on a hot day.
Li leveled at 1-1 with more ease but both players started within themselves as the importance of the occasion sank in.
Li showed remarkable tenacity by breaking immediately at the start of the second set with more lusty blows and then saving a break point against her in the following game.
Schiavone tried desperately to get a foothold, fending off numerous break points.
The wasted opportunities looked like proving costly for Li as she suddenly looked rattled and blazed a forehand wide to allow a pumped-up Schiavone to haul herself back to 4-4, much to the delight of her vocal fans.
With Li serving at 5-6 and the crowd eagerly anticipating a deciding set, Schiavone lost her cool when she ranted over a line call, pointing angrily at a mark in the clay.
Had that decision gone her way she would have earned a set point. Instead Li remained calm, held serve to set up a tiebreaker and with clearly no appetite for tea-time drama, reeled off seven consecutive points.
(Editing by Clare Fallon)