The unseeded 26-year-old, who defeated third seed Garbine Muguruza in round two, held off a late fightback from Konta to reach the last eight of a grand slam for the first time.
Sevastova was out of the game for 20 months until the start of last year, having announced her retirement in May 2013 after a series of injuries.
“It was hard moments for me in 2013,” the 48th-ranked Sevastova said. “I was injured and not having fun and I was kind of depressed, but now I’m back.”
In a topsy-turvy match, containing 12 breaks of serve, Sevastova had match point at 5-3 and another at 5-4 only for Konta to break back for 5-5.
But the Latvian regained her composure in time to hold serve and then break Konta, who was appearing in the last 16 for the second consecutive year, to clinch victory.
Konta was bidding to become the first British woman to reach the quarter-finals in New York since Jo Durie in 1983.
(Editing by Ken Ferris)
