The two-time defending champion at Flushing Meadows was broken three times in her first four service games as Townsend threatened an upset. Sabalenka then found her range, held her remaining service games and closed out the match in straight sets.
It was the first meeting between the pair. Townsend’s net play and returning caused problems in the opening set, but she could not maintain the same pressure after Sabalenka settled.
“Basically, I was just trying to stay focused on myself and play not only point by point but ball by ball,” Sabalenka said. “I’m happy that I was able to turn it around in that second set.”
The Belarusian praised her opponent afterwards.
“I’m happy to be through this really tough opponent,” she said. “What an incredible player she is, approaching the net. What a great returner: moving well, very brave. You could see how focused she was. It was really challenging playing her.”
Sabalenka next faces either Wimbledon champion Linda Noskova or Ukraine’s Marta Kostyuk for a place in the semi-finals.
The result keeps the top seed on course for a third successive US Open title. Townsend, a dangerous floater with a distinctive serve-and-volley style, pushed her harder than the scoreline suggests. Once Sabalenka began landing first serves and dictating from the baseline, the American’s openings disappeared.
Sunday’s win was another step in a campaign that has already included a first-round interruption when Sabalenka complained about the smell of cannabis on court. The tennis itself has been more straightforward since. She remains the player to beat in New York.