The result means that six of the top 10 women in the seedings have been sent packing even before the second round is completed.
The 26-year-old Jeanjean, ranked No.227, is a former big hope of French tennis who ended up living on minimum wage after a knee injury suffered when she was 15 kept her off the courts for two years.
Dropped by Nike, who had given her a 10-year sponsorship deal, and by the French federation, who had assigned her a full-time coach when she was 12, Jeanjean went to study in the United States at the Lynn University in Florida.
She came back to tennis after five years in the US only for her return to be slowed down by the COVID-19 pandemic.
"I lived on minimum wage and I didn't live from day-to-day, but week after week. I put all the money I had into a week's worth of tournaments and if they went well I got another week, but if they went badly I didn't play for two months because it was financially impossible," she said.
On Thursday, Jeanjean outfoxed eighth seed Pliskova, a semi-finalist at Roland Garros in 2017, to get into the third round.
Pliskova made 28 unforced errors and was broken in half of her eight service games.
"I could not try to overpower her, it was impossible, so I had to try to derail her and it worked perfectly," she said.
"I don't have an explanation. I don't even realise what's happening. I know I'm 26. It's my first Grand Slam. I thought I would have lost in the first round in two sets, and I found myself beating a top-10 player," Jeanjean said.
"So honestly, I have nothing else to say. I don't really know how it's possible, what's happening. I just try to give my best to play my tennis, and it's working so far."
Pliskova joins No.2 seed Barbora Krejcikova, No.4 Maria Sakkari, No.5 Anett Kontaveit, No.6 Ons Jabeur and No.10 Garbiñe Muguruza on the way out.
The remaining four women in the top 10 are scheduled to play on Thursday: No.1 Iga Swiatek, No.3 Paola Badosa, No 7 Aryna Sabalenka and No.9 Danielle Collins.
Jeanjean, whose early rise had drawn comparisons with Martina Hingis, will next face Russian Ekaterina Alexandrova, the 30th seed, or Romania's Irina-Camelia Begu.
With The AP
