The 34-year-old Canadian of the EF Education team was from the morning breakaway that managed to resist the return of the group of favorites, delayed by the falls.
This is by far the best victory of the career of the Canadian, very active in the breakaway.
"It's unreal, I have no words. It's a dream come true," she said, overwhelmed by emotion.
"I wanted to weigh in on this race, to be at the front. In this kind of race, you have to avoid bad luck, it would have been a shame to lose after such a long breakaway," she added.
Jackson won ahead of Italy's Katia Ragusa (Liv Racin Teqfind) and Belgium's Marthe Truyen (Fenix-Deceuninck).
The two Frenchwomen Eugénie Duval (FDJ-Suez) and Marion Borras (St Michel-Mavic-Auber 93) finished fourth and fifth.
The favourites, including Belgium's Lotte Kopecky (7th), cut the finish twelve seconds behind the winner.
Kopecky, who had just won the Tour of Flanders, was involved in a big crash 36km from the finish when she tried to get back on the morning breakaway with a group of chasers.
The Flemish tried to come back next, approaching with her group to less than ten seconds in the final, but without managing to completely plug the hole.
"The race was very tough, I had some tough moments today," she said.
© 2023 AFP