Wightman, the world champion over 1500m, recorded a personal best time of 1:43.65 to beat Algeria’s Djamel Sedjati.
Five-time world champion Fraser-Pryce lost to compatriot Shericka Jackson.
Armand Duplantis also suffered a shock defeat in the men’s pole vault.
After settling for silver in the European Championships last month, Wightman ran 800m under one minute and 44 seconds for the first time in his career.
Meanwhile, Fraser-Pryce, who set the fourth-fastest ever women’s 100m in July, was beaten by one hundredth of a second in a photo finish against Jackson.
“It takes a lot of hard work to beat Shelley-Ann, she’s a tough cookie to beat,” Jackson said after her first win in the Diamond League this season.
“Tonight I had a good execution, probably not perfect but it paid off in the end.”
Fraser-Pryce, who pulled out of the last Diamond League meet in Lausanne with a hamstring injury said she would “listen to my body” before deciding on whether to run in next week’s final event in Zurich.
Sweden’s world, Olympic and European pole vault champion Duplantis was beaten for the first time since August 2021 as he lost out to Ernest Obiena of the Philippines after failing to clear a height of 5.91m three times.
“I am human and I make mistakes and I definitely did some today. I didn’t find good rhythm on the runway today,” Duplantis said.
Elsewhere, Ireland’s Ciara Mageean claimed a new national record in the women’s 1500m when she beat Britain’s Laura Muir across the line with a time of 3:56.63 – her first time running the distance under four minutes.
Kenya’s Jacob Krop recorded the best time in the world this season in the men’s 5,000m as he claimed victory with a personal best time of 12:45.71, beating Grant Fisher, who broke the American record.
American Kara Winger, who is set to retire at the end of this season, threw a world-leading javelin distance of 68.11m, breaking the national record, while Yaroslava Mahuchikh of Ukraine cleared 2.05m to win the women’s high jump and set the best height in the world this season.