The top-seeded Halep dropped four straight games to lose the second set, and staved off a break point in the first game of the third to eventually make her fourth final of the year.
Halep's rise, to a current world No. 3 ranking, helped get the tournament off the ground, and the French Open finalist could yet cap the organizers' dreams in Sunday's final. She has a 3-2 record against the second-seeded Vinci.
Vinci, coming off a Wimbledon doubles triumph, was slowed only by a shower in the second set in beating Kristina Kucova of Slovakia 6-1, 6-3 in their semifinal. Vinci will be playing for her 10th singles title.