Sabalenka slapped winners practically at will past Iatcenko, a 22-year-old qualifier in her first Grand Slam singles main draw.
"Night atmosphere is always the best atmosphere," Sabalenka said.
A four-time Grand Slam champion who has triumphed in New York the last two years, Sabalenka relishes the hard courts of Flushing Meadows.
But she has struggled in recent months, suffering disappointing losses at both the French Open and Wimbledon and turning in middling performances at hard court warm-up tournaments ahead of the US Open.
But against 160th-ranked Iatcenko, she raced to a 5-0 lead before Iatcenko managed to get on the board.
Sabalenka dropped just four points on serve in the opening set and was broken just once to give Iatcenko her only game of the second set. Sabalenka responded by winning the next three to secure the win.
"I'm happy with my level. I've been working really hard, but I feel like I'm moving away from trying to be perfect on court," she said.
"I know that you cannot be perfect, and I'm just trying to work with what I have right now," added Sabalenka, who will play 92nd-ranked Kamilla Rakhhimova of Uzbekistan in the third round.