LONDON -- Wimbledon is the only Grand Slam tournament that schedules all 16 men's and women's fourth-round matches on the second Monday. Here are five matches to watch:
1. SERENA WILLIAMS vs. SABINE LISICKI: If Williams' 34-match winning streak is going to face a real challenge, it might just come from Lisicki, the 23rd-seeded German who upset Maria Sharapova in last year's fourth round at the All England Club and is now working with Kim Clijsters' former coach, Wim Fissette. Williams owns the undisputed best serve of any active woman -- and perhaps of any woman, of any era -- but Lisicki can smack `em, too: Her season ace total ranks No. 2 behind Williams, and she's won 27 of 29 service games this tournament. Lisicki is "dangerous when she dictates points," said Patrick Mouratoglou, the French coach who's been helping Williams during the stretch in which she's won 77 of 80 matches and three of the last four Grand Slam titles.
2. NOVAK DJOKOVIC vs. TOMMY HAAS: After his gut-wrenching, 9-7 fifth-set loss to Rafael Nadal in the French Open semifinals, Djokovic didn't sulk; he came out stronger than ever. For the first time, he reached the second week of Wimbledon without dropping a set, and he made only three unforced errors in the third round. But the top-seeded Djokovic hasn't faced much of a test yet. He could against Haas, who eliminated Djokovic en route to the 2009 Wimbledon semifinals, and also defeated him at Key Biscayne in March, becoming the third-oldest man since 1968 to beat the No. 1 player. If the 35-year-old Haas can do it again, he'll become the oldest Wimbledon quarterfinalist since Tom Okker in 1979. When they met at Roland Garros, though, Djokovic topped Haas in straight sets.
3. ANDY MURRAY VS. MIKHAIL YOUZHNY: Think anyone around here might tune in for this one? Murray is their man, their hope to end a 77-year drought without a British male champion at Wimbledon. He gets loud support from the stands -- and also loud groans when he misses a makeable shot. Murray's popularity skyrocketed when he bared his emotions and teared up during his runner-up speech after losing to Roger Federer in last year's Wimbledon final, so imagine how big a deal he became a month later when he beat Federer at the All England Club to win a gold medal at the London Olympics, not to mention when he finally won his first Grand Slam title at the U.S. Open. Murray has won 14 consecutive grass-court matches, and 20 of his past 21, but Youzhny is no pushover. The 20th-ranked Russian reached the final on grass at a tuneup tournament before Wimbledon, was a quarterfinalist at the All England Club in 2012, and twice reached Grand Slam semifinals. He's also a character. He once made himself bleed by hammering himself in his head with a racket; used his foot to write a word of apology in the red clay at Roland Garros during a 6-0, 6-2, 6-2 loss last year; and destroyed a racket at this year's French Open by whacking it nine times against his sideline seat.
4. LUKAS KUBOT vs. ADRIAN MANNARINO: You might never have heard of these guys, but one will be a 2013 Wimbledon quarterfinalist. Kubot is ranked 130th, Mannarino 111th, which is why theirs is the only men's or women's fourth-round match scheduled for Court 14 and its 312 spectators' seats. Their matchup pits one guy who's been serving really well (Mannarino and Djokovic are the only two men who have not lost a service game so far) against another who's been returning really well (Kubot leads the remaining 16 men in percentage of return points won against first serve, 44, and in percentage of return games won, 50). The winner of Kubot-Mannarino faces the winner of Jerzy Janowicz against Jurgen Melzer, so a member of that quartet will end up in the semifinal spot that pretty much everyone figured would belong to Federer or Nadal.
5. SLOANE STEPHENS VS. MONICA PUIG; LAURA ROBSON vs. KAIA KANEPI: OK, so listing two matches here raises the total to six to watch, but they're both worth a mention. Stephens is 20, and both Puig and Robson are 19; the trio represents some of the top up-and-coming talent on the women's tour. "There's definitely a new generation," Williams said. "I feel like this might be the beginning of, maybe, the future. I mean, eventually there's going to have to be a shift." Stephens, an American, is seeded 17th, and into the fourth round for the fourth time in the past five Grand Slam tournaments, including a run to the Australian Open semifinals in January, when she beat Williams. So Stephens must be considered the favorite against Puig, a Puerto Rican who is ranked 65th and playing in only her second major after reaching two junior Grand Slam finals. Robson, meanwhile, is the first British woman in the final 16 at Wimbledon since 1998, and therefore a big crowd favorite -- not to mention someone who's been drawing a lot of attention here for Twitter interactions with members of the popular boy band One Direction. Kanepi, 28, is far more experienced and accomplished at this point, having played in four Grand Slam quarterfinals.