The 30-year-old, runner-up in Paris five years ago, gave the erratic Pliskova no chance on the main Philippe-Chatrier court, speeding through the first set in 49 minutes before the Czech recovered in the second.
But she kept piling up unforced errors -31 in total - as well as half a dozen double faults, giving Stephens, ranked in the past as high as third in the world, the chance to race back from 4-3 down, break her twice and rattle off the next three games to seal victory.
"This is my favourite court in the world and I am super happy to be back," said Stephens, currently ranked 30th.
The American, who won her only Grand Slam at the 2017 US Open, was also a quarter-finalist in Paris last year despite struggling for form.
Stephens came into the tournament in improving form on clay after winning her first WTA 125 event and reaching the semi-finals on clay in Rabat last week.
"To start like that on your favourite court and favourite surface is great. I wanted to get matches under my belt this year (before the tournament) and I was feeling confident," Stephens said.
