The 19-year-old Czech, who made quarter-final appearances at Indian Wells and Miami and reached the final on clay in Istanbul this season, blew the 12th seed off court with a mix of power and guile from the baseline.
Vondrousova tormented a sorry Sevastova with drop shots throughout, bagging the last nine games to advance in searing heat.
She has won all her four matches in Paris within 90 minutes and without dropping a set and on Sunday she followed up her third-round victory against Carla Suarez Navarro with another stunning display.
"I think I had tough last year because I was pretty new to tennis and to the pro scene, so it was tough for me," Vondrousova recalled.
"But now I have found a big team and great coach, so I think that helps me a lot."
She next faces Petra Martic, the woman who beat her in the Istanbul final, after the Croatian 31st seed advanced in much more laborious fashion.
Martic, who career has been hampered by back problems and slipped down to 662nd in the WTA rankings in April 2017, snatched a 5-7 6-2 6-4 win over Estonian Kaia Kanepi.
In a see-saw encounter, Kanepi broke decisively in the 12th game to take the opening set but Martic piled on the pressure as she raced through the second to force a decider.
Both players suffered early jitters as they each dropped serve twice in the first six games.
Martic saved a couple of break points at 4-3 before stealing Kanepi's serve once again to move 5-4 up and serve it out, prevailing on her first match point.
(Reporting by Julien Pretot; Editing by Pritha Sarkar)
