Home favourite Simon battled back to win 3-6 1-6 6-4 6-1 7-5 although he looked like capitulating late on when old warrior Hewitt won five games in a row from 5-0 behind in the decider.
Simon, one of six Frenchmen seeded at this year's championships, screamed at himself to "relax" as Hewitt silenced the crowd on a chilly Suzanne Lenglen court by breezing through the opening two sets.
He finally loosened his shoulders and with 32-year-old Hewitt beginning to look leg-weary, Simon was strolling to victory when he opened up a large lead in the fifth set.
No French player has won the men's singles at Roland Garros since Yannick Noah in 1983 and with each passing year that statistic weighs a little more heavily on the current crop led by sixth seed Jo-Wilfried Tsonga, Richard Gasquet and the 28-year-old Simon.
When he squandered two match points, one when his string snapped and the other when Hewitt got lucky with a net cord, the tension was mounting again, especially with Hewitt's reputation for revelling in five-set dogfights.
For a while the straight-jacket that appeared to be fastened round Simon for the first two sets returned but he recovered some composure from 5-5 and completed his first career victory from a two-set deficit when Hewitt netted a forehand.
"It was very, very complicated in the beginning," Simon said courtside. "Everybody was cheering me on but I could not do anything. At two sets down I started to play better.
"I think I have never recovered from two sets down. Well, now it's done. At 5-0 I had the feeling I was going to win but he started to play better and there were a few close points and then, I got tense."
Former world number one and twice grand slam champion Hewitt has never excelled on claycourts but pushed Simon from side to side for the first half of the three hour 19 minute contest.
Once Simon began to increase the power of his groundstrokes and shake off his inhibitions the match swung quickly.
At one stage early in the fifth set Hewitt needed running repairs on his foot - the various strappings and supports binding his ankle evidence of the punishment his body has taken in 56 grand slam appearances.
The durability that once marked Hewitt out as one of the game's toughest competitors may have waned but the old fire still burns inside and when he surged back in the fifth an incredible victory looked possible.
It was not to be, however, as the weary world number 86 finally succumbed, much to Simon's relief.
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