LONDON » One five-time Wimbledon champion is guaranteed to reach the quarterfinals. Another is assured of elimination.

That’s what will happen Monday when Serena Williams plays older sister Venus Williams for the sixth time at the grass-court Grand Slam in southwest London.

"They’ve been unbelievable for the sport. I’ve said that many times," said Roger Federer, a seven-time Wimbledon champion who will also be playing on Manic Monday. "Their head-to-heads, I don’t know how much that has to do with it. I think it’s more their individual play."

Individually and together, the Williams sisters have become two of the greatest champions at the All England Club. They have each won five singles titles, and have teamed up to win five more in doubles.

Against each other on the grass at Wimbledon, Serena leads 3-2, with all three of her wins coming in finals. Venus won one final, and also won a semifinal match against her younger sibling in 2000 — the first time they met on court at the tournament.

Although Serena is still at the top of her game and going for a true Grand Slam this season, Venus has been struggling for the past few years and was diagnosed with an energy-sapping autoimmune disease in 2011, three years after her last Wimbledon title. It was the previous year, in 2010, when she last reached the quarterfinals at Wimbledon.

But this year, Venus has been nearing her past high standards, winning all three of her matches in straight sets.

"She’s playing so well," Serena said. "I’m practicing next to her every day and I’m in awe of how she’s doing. It’s a little frustrating because I know I have to play her."

The Williams matchup is just one of the 16 fourth-round matches on the schedule for Monday — eight for the men and eight for the women.

Here are some things to know about Monday’s matches:

ROGER’S RECORD

Roger Federer is the only current player with more Wimbledon singles titles than a Williams, and the seven-time champion is one away from a record-setting eighth.

Federer has had a relatively straightforward first week, winning his first two matches in straight sets and his third in four. His next opponent is 20th-seeded Roberto Bautista Agut, a Spaniard who is playing at Wimbledon for the third time and has never reached the fourth round.

But for Federer, the pursuit of No. 8 and breaking the tie with Pete Sampras and 1880s player Willie Renshaw doesn’t seem to be the only thing spurring him on.

"This is more something like you talk about for a couple weeks, it’s gone again, then you have to wait a year if you don’t do it," Federer said. "I just take Wimbledon as such, what a huge tournament it is, what an opportunity it is."

SEMIFINAL POSSIBILITY

Maria Sharapova and Victoria Azarenka, the other two Grand Slam champions in the fourth round, have been two of the most consistent players at this year’s tournament, and another pair of wins for each would set up a semifinal meeting on Thursday.

Sharapova, the 2004 Wimbledon champion, has lost only 15 games through three rounds and will next face Zarina Diyas of Kazakhstan. Azarenka, a two-time Australian Open champion, has lost 17 games and will next meet 30th-seeded Belinda Bencic of Switzerland.

Sharapova has played Diyas once before, beating her 6-1, 6-1 in the third round at this year’s Australian Open.

"You can’t underestimate anyone’s level," Sharapova said.

GO GO DJOKO

Novak Djokovic missed out on a chance to make a run for a true Grand Slam when he lost to Stan Wawrinka in the French Open final. But the top-seeded Serb can still defend his title at Wimbledon, a victory that would give him a third championship at the All England Club.

"I try to put myself only in the present moment, not fight against the thoughts and the pressure and the excitement," Djokovic said, referring to his past experiences at the grass-court major.

Djokovic’s next opponent will be Kevin Anderson, a 14th-seeded South African who has never been past the fourth round at a Grand Slam tournament.

MAJOR MISSION

Four women who have come close but are still looking for their first major title will also be on court Monday: Caroline Wozniacki, Agnieszka Radwanska, Lucie Safarova and Jelena Jankovic.

All four of them lost to 20-time major champion Serena Williams in Grand Slam finals.

Wozniacki lost to Serena in the 2014 U.S. Open final, Radwanska was beaten in the 2012 Wimbledon final, Jankovic in the 2008 U.S. Open final and Safarova in this year’s French Open final.

Wozniacki also reached the U.S. Open final in 2009, losing to Kim Clijsters.