The Ukrainian is yet to drop a set this tournament.
Ukrainian Svitolina is yet to drop a set this fortnight and recovered from a break down to take the first against the 12th seed.
Halep hit back from one break down in the second but Svitolina broke the Romanian’s resistance by converting a third break point to win a pivotal seventh game.
The Olympic bronze medallist, still searching for a first grand-slam title, went on to wrap up a 6-3 6-3 vitória.
“It was a great match, I was excited going into it because I know what a big fighter Simona is,” Svitolina said in her on-court interview.
“I knew I would have to play my best and I’m extremely happy with the win.”
Defeat continued a below-par set of results for Halep at Flushing Meadows as she was in the second week for only the second time and has just one semi-final appearance to her name in 2015.