Sabalenka and Pegula arrived in New York as the two most in-form players, with each having won a WTA 1,000 tournament last month.
Pegula appeared to be brimming with confidence as she started aggressively and surprised Sabalenka by striking the first blow early in the opening set.
But Sabalenka broke back immediately before powering her way through the next three games.
The two-time Australian Open winner faltered, however, when trying to serve out the set and Pegula put a finger to her ear, demanding more noise from an already-raucous crowd, as she refound her rhythm to level the opener at 5-5.
The pair grew frustrated as the first set came to a crescendo, with both hitting their racquets angrily off the floor before Sabalenka – after missing four set points – closed it out at the fifth time of asking.
Keen to avoid a repeat of last year’s final, which she lost after winning the opening set, Sabalenka steamrolled through the first three games of the second set.
But roared on by her home crowd, Pegula battled her way back, breaking twice to take a 5-3 lead before the big-hitting Sabalenka slammed on the brakes.