Li Na fought back to beat German Angelique Kerber 1-6 6-3 6-1 to take the Cincinnati Open title.
Germany's Kerber won the first set comfortably but the Chinese ninth seed won 11 of the last 12 games to seal a sixth WTA title of her career.
The 30-year-old's win comes six days after she was beaten in the final of the Montreal Cup by Petra Kvitova.
Kerber, 24, has enjoyed an outstanding year but once Li got back into the second set she coasted to victory.
Wimbledon semi-finalist Kerber, who has moved up to seventh in the world rankings this year, won the first set with ease and moved 3-1 ahead in the second.
2011 French Open champion
Li broke to level and when she did so again to move 5-3 ahead Kerber's resistance crumbled and she managed just one more game in the match.