The 48th-ranked Sevastova survived some late nerves to close out the world number three from Spain 7-5, 6-4 and set up a third-round clash with Ukrainian Kateryna Bondarenko, a 5-7, 7-6 (7/5), 7-5 winner over China’s Zheng Saisai.
“I was shaking a little bit at the end,” admitted 26-year-old Sevastova, who stepped away from the game in 2013, tired of dealing with injuries.
She returned in 2015, and reached WTA finals in Mallorca and Bucharest this year.
Her victory cost Muguruza her slim chance of overtaking Serena Williams atop the world rankings, and the magnitude of her biggest win on one of the game’s biggest stages wasn’t lost on Sevastova.
“On Ashe (court), a night match, what’s going to be bigger,” she said.
For Muguruza, it was another early exit at Flushing Meadows, where she was also eliminated in the second round last year.
“I don’t know,” she said of her lack of success in New York in four main draw appearances. “I try to give it all. I try to fight on court. She was just better. I don’t know if it’s bad luck. No, I don’t think so.
“Well, I did my best result again,” she added with a smile.
Although she didn’t think she played her best tennis, Muguruza wasn’t beating herself up over that.
“It’s very rare when you play your best,” she said. “Today was just very difficult. Everything I was trying to do she was coming back and doing incredible shots.”
The Spaniard said there was nothing to do now but try to regroup for the WTA tour’s late-year events in Asia, where she won the premier level tournament Beijing last year which was her biggest title until she stunned Williams in the championship match at Roland Garros in June.
“Even though today is not my favorite match, this is not going to stop me from resting some days and going back to Asia and trying to do like last year,” she said.