With the weight of expectation on her shoulders as France waits for its first Roland Garros singles champion since Mary Pierce lifted the Suzanne Lenglen Cup in 2000, fifth seed Garcia got off to a shaky start.
But she made her experience count in a first-set tiebreak, which she won with a booming ace and a brutal forehand down the line.
Wang, however, continued to go for her shots and was rewarded with an early break in the second set, holding on to it to level the match.
Serving to stay in the contest at 5-4 in the decider, Wang cracked and bowed out when she sent a forehand long.
"Being here means a lot to me," said Garcia.
"When I was coming here before I would see the fans cheering for the French but I was closing myself up and could not take the energy from the crowd," the WTA Finals champion, who also reached the semi-finals at the U.S. Open last year, added.
She next faces Russian Anna Blinkova (24).