Twin challenges for Federer at US Open

Sleeping patterns are vital to top tennis players, so new father of twins Roger Federer knows he has his work cut out as he bids to become the first man in 84 years to win six straight US Opens.

Federer on Saturday kept his campaign to match Bill Tilden on track with a 4-6, 6-3, 7-5, 6-4 third-round win over old foe Lleyton Hewitt, also a father, and then took the time out to reflect on his new paternal responsibilities.

"We have a good setup. Mirka is great. She works extremely hard," Federer said of his wife, who gave birth to twin girls in July, shortly after Wimbledon when her husband became the all-time Grand Slam title record holder with 15.

"She's tired during the day but she has also some help, has a little bit of life, and also can come and watch me play and get outside a little bit. That's important," Federer said.

"Sure, I'm losing sleep but that's part of it. I make sure on my off day maybe I do get a night where I can sleep in longer or take an afternoon nap. It's working out OK."