Halep, ranked third in the world, was more consistent from the start and easily took the first set.
The 31-year-old Vinci lost her serve to trail 4-2 in the second before Halep won the final game to love and clinched the title in under 70 minutes.
Halep now leads Vinci 3-2 in head-to-heads.
The 22-year-old Halep is enjoying the best year of her career. She was runner-up in the French Open and reached the semifinals at Wimbledon.