The win moved Halep into Sunday's final against the victor of a Saturday evening match between third-seeded Sloane Stephens of the United States and defending champion Elina Svitolina of Ukraine.
Sloane Stephens set up a rematch of the French Open final with Halep after she eased past defending champion Elina Svitolina 6-3 6-3.
American Sloane Stephens faced little resistance in her 6-2 6-2 win over Latvia's Anastasija Sevastova in a match that took a little over an hour to complete.
Barty will play the Romanian for the first time after dispatching Kiki Bertens 6-3 6-1 in less than an hour to extend her ideal record over the Dutchwoman to two matches.
"I think I played smart tennis today", Halep said.
Halep had two further chances to claim the victory Stephens' serve, only for the American to produce further impressive resistance to hold.
The French Open champion showed no signs of fatigue following her marathon three-set win over Anastasia Pavlyuchenkova on Wednesday, running down balls to extend points and wear down the slower Garcia. Svitolina, playing in her third tournament in North America this season, increased depth and range off the forehand side to level at 4-4. I got better than the last final we played.
She noted Barty had extra rest because she played the first match Friday afternoon. "I made semis back to back, then ended up winning the U.S. Open, so I don't really think there's such a thing". But I feel great. (On Thursday), I played two matches.
"That was kind of the goal for me to keep that consistency, a good level of tennis to cement my spot in the top 20".
Halep said on court afterwards: "It's been an fantastic week and I feel like I reached my best level of tennis". I think it really helped me to get back my rhythm, and then I was just going more and more for my shots. It certainly lived up to expectations, as Roland Garros victor Halep fended off four set points to claim the opening set. "Obviously, in a final, you hope for matches like that - super competitive, high energy".
After Stephens won the second set, Halep took control in the third, jumping out to a 5-2 lead. I still have to play five more tournaments.
Down 4-1 in the first set, Stephens came storming back to force a tiebreaker.
Stephens could now prepare more confidently the title defence in NY, as she said yesterday.
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