Sabalenka and Alexandrova walked onto Arthur Ashe Stadium with fans still catching their breath after Alexei Popyrin upset defending champion Novak Djokovic late on Friday night, and the duo began their match only at 00:08 local time.
The previous latest recorded start at the tournament came in 1987, when Gabriela Sabatini and Beverly Bowes took to the court at midnight and wrapped up in 90 minutes.
A quick finish seemed unlikely after Australian Open champion Sabalenka's game went off the rails amid a string of unforced errors and the second-seeded Belarusian dropped the opening set in 33 minutes.
"I don't know what I did, I was just trying to stay low, put as many balls as I can back on that side. She played incredible tennis in the first set. It was really tough to change it," Sabalenka said.
She quickly found her groove and broke for a 3-1 lead in the next set and never looked back thereafter, levelling the contest with a breathtaking display of power to overwhelm her spirited Russian opponent.
"I'm really happy I was able to turn around this match and get this really difficult win."
Sabalenka was surprisingly broken after going up 5-0 in the decider but she promptly delivered the knockout blow to a fading Alexandrova with a backhand winner to delight the crowd that stuck around.
"Thanks so much for staying that late," Sabalenka said as the clock neared 02:00.
