The five-time Grand Slam champion, a tournament wild card, overcame a first-set deficit to beat the Belarusian teenager and celebrate her first title since she won the Italian Open in May 2015.
Sharapova, who made her comeback in April, trailed world No. 102 Sabalenka 4-1 and 5-1 in the first and second sets, respectively. But the 30-year-old Russian, who did not drop a set en route to Sunday's final, fought back on each occasion to claim her first title in 29 months.
Sharapova served a 15-month ban after she tested positive for the banned substance meldonium.
The former world No. 1 was denied a wild card for the French Open before missing Wimbledon because of injury.
She was granted a wild card for the US Open and reached the fourth round before losing to Latvia's Anastasija Sevastova.