Former champions Novak Djokovic and Roger Federer will set up a mouth-watering US Open quarter-final if they win their matches on Monday.

Sixth seed Djokovic faces Portuguese Joao Sousa in the fourth round, while Federer plays Australian John Millman.

The former world number ones have not faced each other so early in a Grand Slam since 2007, when Federer won to reach the Australian Open last eight.

First Djokovic must beat Sousa, making his debut at this stage of a Slam.

The world number 44 has already knocked out two seeds – Frenchman Lucas Pouille in the third round and Spain’s Pablo Carreno Busta in the second.

“He’s a fighter, he’s a grinder,” Djokovic said. “He will not hand you the victory, you’ve got to earn it.”

Federer’s opponent Millman, the world number 52, is also competing in unknown territory after knocking out 14th seed Fabio Fognini in the second round.

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Sharapova enjoying the nights

Also competing on Arthur Ashe Stadium is Russian 22nd seed Maria Sharapova, who is up against Spanish 30th seed Carla Suarez Navarro in the fourth round.

The five-time Grand Slam champion is looking to extend her perfect record of 23 wins in the night session at Flushing Meadows.

The 2006 US Open winner reached the quarter-finals of the French Open earlier this year but has not gone beyond the fourth round in New York since 2012.

“It’s the energy you get, no doubt I feed off this energy,” Sharapova, 31, said.

“I don’t remember how old I was when I played my first night match, but I’m sure I was young enough to still be intimidated by the city and the lights and the atmosphere, the noise.

“But I really turned that around. I think I thrive on that. I love the atmosphere. I love that they know how to cheer hard. I thrive on playing under the lights for some reason. I love that.”

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Also in action…

Last year’s runner-up Madison Keys faces Slovakian 29th seed Dominika Cibulkova on Arthur Ashe before Djokovic’s match with Sousa.

Japanese 21st seed Kei Nishikori takes on German Philipp Kohlschreiber on Louis Armstrong, before compatriot Naomi Osaka faces 26th seed Aryna Sabalenka of Belarus.

And seventh seed Marin Cilic, the 2014 champion, is up against Belgian 10th seed David Goffin in the last match of the evening.