Cornet, ranked 37, took advantage of an error-strewn performance from her Polish opponent to win 6-4, 6-2 on Court 1 in their third-round tie.
Swiatek made a total of 33 unforced errors in an uncharacteristically sloppy display, compared with just seven by Cornet. In reaching the fourth round, the French player matched her run at Wimbledon in 2014, when she beat Serena Williams in the third round. "I have no words right now," she said. "It reminds me of the time I beat Serena on the same court eight years ago exactly.
This court is a lucky charm for me." Cornet said she felt Swiatek could be vulnerable on grass after pulling off the biggest shock at Wimbledon so far.
The 32-year-old reached a career milestone by defeating former number one Simona Halep to advance to her first major quarter-final at the Australian Open earlier this year. "I'm like good wine," said Cornet, who is contesting her 62nd consecutive Slam, matching Ai Sugiyama's record. "In France good wine always ages well, that's what's happened to me.