The American, who has dropped just four games in four sets so far in the tournament, breezed past Galina Voskoboeva 6-3 6-0 at Flushing Meadows on Thursday.
Despite being without a day off so far at the Grand Slam, Williams believes that she is used to the demands of her hectic diary.
"I usually play every day," she said when asked if the busy schedule bothered her.
"In regular tournaments I don't have a day off. Only in the grand slams I get the luxury of having a day off. I guess I didn't get that, [but] I'm definitely used to it."
Williams will meet Yaroslava Shvedova in next round on Friday.