NEW YORK — Yet to be challenged even a tiny bit at this U.S. Open, Serena Williams now gets a sure-to-be-hyped match against one of only three women to beat her all year, Sloane Stephens.

From the moment the women’s draw came out at Flushing Meadows, it was clear which potential fourth-rounder was the most intriguing: defending champion Williams against up-and-coming talent Stephens.

“As I always say, I think it will be epic,” Stephens said. “I’m really looking forward to it. See what happens.”

And that statement came hours before Williams even had advanced out of the third round by beating 78th-ranked Yaroslava Shvedova of Kazakhstan 6-3, 6-1 in a match that wrapped up at 1:05 a.m. Saturday.

“I’m so excited you guys stayed out for the late-night rendezvous. Thank you, guys, for staying,” Williams told the Arthur Ashe Stadium crowd. “I don’t think I’ve ever played this late.”

She has dropped a total of eight games through six sets this week. Against Shvedova, she hit serves at up to 119 mph, and produced a 22-3 edge in winners.

Much, much earlier, on a ho-hum afternoon devoid of any truly significant surprises, Stephens reached the round of 16 in New York for the first time by beating 23rd-seeded Jamie Hampton 6-1, 6-3 on Friday.

“Serena is the No. 1 player in the world. She’s possibly the greatest player of all time. Sloane is Sloane. You know, she’s making her own name. She’s top 20 in the world for a reason,” Hampton said. “They’re both great players, both great competitors.”

Hampton’s blase summation of a Williams-Stephens matchup: “I don’t really make too much of it.”

She might be the only one.

“It’s something,” Stephens said, “I think everyone is looking forward to.”

And why not? Williams is 32, seeded No. 1, and owns 16 major titles. Stephens is 20, seeded 15th, and already carrying the label of “Next Big Thing” in American tennis.