Top-seeded Jabeur sent packing in San Diego as Garcia advances
Potapova, ranked 27th in the world, said patience was the key to her 6-4, 7-6(4) victory over world number seven Jabeur, who reached her third Grand Slam final at Wimbledon this year.
"Ons is very tough to play," said Potapova, who had edged Alycia Parks in three sets in the first round as Jabeur enjoyed a first-round bye.
"She is truly one of the best in the world and with her style it's very uncomfortable. She likes to mix it up a lot, and actually I'm really proud of myself today that I was able to stay calm, focused and just do what I've got to do."
Jabeur was coming off a fourth-round showing at the US Open, where she battled illness in the opening rounds.
Potapova notched her sixth career victory over a top-10 player and lined up a quarter-final meeting with 2020 Australian Open champion Sofia Kenin, a 1-6, 6-4, 6-2 winner over fellow American Katie Volynets.
Potapova converted six of her 11 break chances, breaking the Tunisian at love to seal the opening set.
Jabeur served for the second set at 6-5 but was broken, Potapova racing to a 4-0 lead in the tiebreaker before Jabeur bore down to knot it at 4-4.
Jabeur's ninth double fault of the match gave Potapova a double match point, and Jabeur fired wide with a forehand to end it.
France's Garcia served up eight aces in her 6-3, 3-6, 6-1 victory over former US Open champion Sloane Stephens, avenging a loss to the American last month in Cincinnati, where Stephens ended the French player's title defence in the second round.
Garcia next faces American Danielle Collins, who beat Latvian Jelena Ostapenko 2-6, 6-3, 6-4.
Third-seeded Maria Sakkari of Greece also reached the quarter-finals, moving through when Camila Osorio of Colombia retired from their match with a right thigh injury while trailing 6-3, 2-2.
