Pegula, whose US Open tune-up included a triumph in Montreal just over two weeks ago, earned a 6-2, 6-2 victory over Italy's Camila Giorgi shortly after 2017 runner-up Keys beat Dutchwoman Arantxa Rus 6-2, 6-4.

An American woman has not won the US Open since Sloane Stephens beat compatriot Keys in the 2017 final but Pegula has shown she just may be hitting her stride at the perfect time after making light work of world number 52 Giorgi.

"I think we are all hoping that we hit the right form going into a slam, especially if you get through the first week trying to hit that stride in the second week," Pegula said during her on-court interview in Arthur Ashe Stadium.

"But you never really know what's going to happen. Tennis is so day-to-day, you can feel great one week and then you can feel terrible the next. So you are just tying to really get through the first few rounds and try and get better each match."

Pegula showcased top-quality footwork and movement as she went up a double-break for a 5-2 lead in the opening set before serving out with a hold to love that she punctuated with a stinging backhand winner down the line.

In the second set, Pegula struck first when she converted her seventh break chance of a 26-point game that lasted 18 minutes to open up a 3-2 lead and then broke again before closing it on her serve with a hold to love.

At Louis Armstrong Stadium, Keys went up a double break for an early 3-0 lead en route to sealing the opener in 32 minutes and never looked back as the American 17th seed got the break she needed for a 3-2 lead in the second before relying on her serve the rest of the way.