Roger Federer, Rafael Nadal and 15-year-old Coco Gauff eye Wimbledon quarterfinal

Roger Federer, Rafael Nadal and Novak Djokovic share top billing on 'Manic Monday' at Wimbledon with teenage sensation Coco Gauff. Eight-time champion Federer, four-time winner Djokovic and Nadal, a double champion, all play last 16 ties against opponents who have never before progressed this far. Federer, the second seed, tackles Italy's world number 20 Matteo Berrettini in what will be the Swiss great's record 17th fourth-round appearance at the All England Club.

"I don't know him very well, so that makes it a bit more tricky," said Federer, chasing a 21st Grand Slam title. Nadal, the champion in 2008 and 2010, also has an unexpected opponent in the shape of world number 69 Joao Sousa, the first Portuguese player to reach the fourth round at Wimbledon.

Nadal has a 2-0 career advantage over the 30-year-old Sousa, with both wins coming on clay. "He's a super dangerous opponent against everybody. He is very quick, has a very good physical performance," said Nadal, looking to back up his 12th Roland Garros title with a third Wimbledon.

Djokovic faces grasscourt rookie

Djokovic insists he will not be complacent about his chances of reaching the final for the sixth time.

The highest seed that the world number one can face before the final is number 15 Milos Raonic, the 2016 runner-up from Canada.

But first up for the defending champion and a 16-time major winner is 21-year-old Ugo Humbert from France who is playing in his first Wimbledon.

Until this year, world number 66 Humbert had never played a grass court match either as a junior or professional. Should Djokovic emerge triumphantly, he would face either Belgian 21st seed David Goffin or Spanish veteran Fernando Verdasco in what would be his 11th quarter-final at the tournament. Raonic, beaten by Andy Murray in 2016 final, has made the quarter-finals in the last two years.

So far at this Wimbledon, he has fired 59 aces across three rounds and dropped serve just once. Raonic tackles Argentine 26th seed Guido Pella who has reached the last 16 at a Slam for the first time -- at the 20th attempt.

The 29-year-old Pella knocked out last year's runner-up and fourth seed Kevin Anderson in the third round. Roberto Bautista Agut, the Spanish 23rd seed, faces French 28th seed Benoit Paire with both men aiming to make the quarter-finals for the first time. Monday's other ties see 2017 semi-finalist Sam Querrey face last-16 debutant and US compatriot Tennys Sandgren.

Japan's Kei Nishikori, a quarter-finalist in 2018, tackles Mikhail Kukushkin of Kazakhstan. Nishikori recorded his 400th tour victory when he beat Steve Johnson in Saturday's third round.

'Keep it up'

In the women's fourth round, 15-year-old Gauff must overcome the former number one Simona Halep.

"I feel like I've always been confident in myself," said 313-ranked qualifier Gauff who shocked five-time champion Venus Williams in the first round. Seven-time champion Serena Williams believes her teenage compatriot could go the whole way.

"I think there are some 15-year-olds, like me, who wouldn't know what to do at Wimbledon," said Williams. "Then you have a 15-year-old like Coco who knows what to do."

Australia's world number one Ashleigh Barty looks in ominous form and although she lost on the grass on the only previous occasion she played last 16 opponent, Alison Riske, it was three years ago. Williams may also be hitting form at the right moment as her win over Julia Goerges on Saturday was by far the most impressive performance of her three matches.

The 37-year-old, who is still tantalisingly one away from equalling Margaret Court's haul of 24 Grand Slam titles, faces Spaniard Carla Suarez Navarro.  "I just need to keep it up," said Williams.

Williams will play Barty in the last eight if both come through Monday's matches. Two-time Wimbledon champion Petra Kvitova plays Britain's Johanna Konta in what will be her first appearance in the last 16 since 2014 when she won the second of her titles.

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HIGHLIGHTS

• Coco Gauff faces world number one Simona Halep in the fourth round.
• Roger Federer is bidding to win his ninth Wimbledon title.
• Rafael Nadal has won the French Open 12 times.