What to watch on day eight of the 2014 US Open

With Maria Sharapova's loss at the US Open, four different women will win Grand Slam titles this year.

Serena Williams takes the next step toward trying to fill out that list when she plays her fourth-round match on Monday. First things first, though. The 17-time Grand Slam champion has yet to even reach a major quarter-final this season.

"I've been a casualty this whole year at Grand Slams," she said after Saturday's third-round victory. "I'm just hoping to keep staying in there."

The two-time defending champ has been locked in so far. Of the 16 women who reached the fourth round, Williams had dropped the fewest games (11).

"So far," Williams cautioned. "Key word."

The top-ranked Williams finally faces an opponent who isn't a fellow American, taking on Estonia's Kaia Kanepi. Kanepi, ranked 50th, upset 2011 US Open champ Sam Stosur and 15th-seeded Carla Suarez Navarro.

She's 5-0 in her career in this round of Grand Slam tournaments, although her previous opponents weren't exactly of Williams' caliber. In fact, she faced an unseeded player in four of those matches, beating 18th-ranked Yanina Wickmayer at the 2010 US Open.

And Williams is perfect at the US Open against players of Kanepi's caliber. Eight of her nine career losses at Flushing Meadows were to top-10 opponents, and the one exception comes with a big asterisk: Kim Clijsters was a major champion returning from retirement.

Rain is again in the forecast for Monday.

Here are some other things to watch on Day 8 at the year's last Grand Slam tournament:

AZARENKA ASCENDING: Victoria Azarenka is starting to look like the player who lost to Williams in the last two US Open finals. Seeded 16th after an injury-mired season, the two-time Australian Open champ has dropped just eight games in her last five sets.

And now she gets to face an opponent who has never experienced anything like this. Aleksandra Krunic, 21, had played one Grand Slam match before this year's US Open.

The 145th-ranked Serb, who upset Wimbledon champ Petra Kvitova in the third round, is seeking to become the first qualifier since Barbara Gerken in 1981 to reach the US Open quarter-finals. She'd also become the lowest-ranked quarter-finalist in the tournament's history (not counting players who didn't have enough matches to earn a ranking).

LAST WOMEN STANDING: Seventh-seeded Eugenie Bouchard is the only woman in the top eight other than Williams who remains alive. She plays 17th-seeded Ekaterina Makarova on Monday.

In the day's other women's match, Australia's Casey Dellacqua, seeded 29th, seeks to reach her first career major quarter-final when she faces 11th-seeded Flavia Pennetta.

MURRAY'S TOUGH ROAD: Andy Murray's ranking slipped after back surgery, which means some touch matchups at earlier stages of tournaments. So the eighth-seeded Murray's fourth-round opponent Monday is ninth-seeded Jo-Wilfried Tsonga.

Murray had won eight straight in the series before Tsonga's victory in Toronto in mid-August, part of a tournament title run for the Frenchman that also included victories over Novak Djokovic and Roger Federer.

The winner of the Murray-Tsonga match could face the top-ranked Djokovic in the quarter-finals. He plays 22nd-seeded Philipp Kohlschreiber on Monday in Djokovic's first match in Louis Armstrong Stadium since the fourth round in 2012.

In other men's matches, fifth-seeded Milos Raonic and 10th-seeded Kei Nishikori meet in this round for the second straight Grand Slam tournament; Raonic won in four sets at Wimbledon. Third-seeded Stan Wawrinka, the Australian Open champ, takes on an opponent who have given him trouble in 16th-seeded Tommy Robredo.

BELLIS IS BACK: A first-round juniors match on the Grandstand, the tournament's third-largest court? Yes, when it stars the darling of the US Open.

CiCi Bellis plays Monday, four days after her run in the main draw ended. The 15-year-old American upset 12th-seeded Dominika Cibulkova, the Australian Open runner-up, in the first round. She lost in the second round Thursday, with fans waiting in line for hours to get in to see the match.

Bellis is the top-seeded girl in the junior tournament. She opens against Renata Zarazua of Mexico.