W2W4: Andy Murray, Serena Williams face toughest tests yet

— -- NEW YORK -- The business end of the season's last Grand Slam is approaching and, thankfully, most of the top seeds are still alive. Wednesday offers four fascinating, mostly marquee matches, with the winners advancing to the semifinals:

Watch every match

At 11 a.m. ET, all play on the outer courts (juniors and doubles) will begin on ESPN3. Click to watch?multicam.?

At noon ET, ESPN and WatchESPN begin coverage of Wednesday's quarterfinal matches. Click to watch.?

To view starting times of upcoming days at the US Open, click here.?

Live scoring

Our real-time scoreboard, updated stats and social handles can be found on one spot: US Open CourtCast.?

Schedules?

Here's a schedule of who's playing Wednesday. Click here.

Wednesday key matches

No. 10 Karolina Pliskova versus Ana Konjuh, noon ET on Arthur Ashe Stadium ( Watch)

This one is the outlier. Konjuh, an 18-year-old from Croatia, has been a revelation, knocking off No. 20 seed Kiki Bertens in the first round and No. 4 Agnieszka Radwanska in the fourth. The WTA's No. 92-ranked player only made it to the second round of the season's previous three majors. Pliskova will be a tougher out, however. Her 29 aces are tied for second among women, and she took out No. 6 seed Venus Williams in a terrific three-set match in the fourth round. Pliskova and Konjuh have never met.

No. 2 Andy Murray versus No. 6 Kei Nishikori, following Pliskova-Konjuh ( Watch)

This was the quarter, based on seeds, that the draw foretold. After a scratchy third-round win over Paolo Lorenzi, Murray crushed lackadaisical No. 22 seed Grigor Dimitrov in the fourth round, dropping only five games. Nishikori, a finalist here in 2014, has played three four-set matches. Murray leads the head-to-head 7-1, including wins in their past four matchups. Murray scorched Nishikori in Rio de Janeiro a few weeks ago.

No. 1 Serena Williams versus No. 5 Simona Halep, 7 p.m. ET on Arthur Ashe Stadium ( Watch)

This is another quarter bracket that played true to form. Williams can't remember ever serving so consistently, and she has yet to lose a set in her quest to keep the No. 1 ranking. Halep has dropped only one set. She was impressive in dispatching No. 11 seed Carla Suarez Navarro in the fourth round. The history between these two has been one-sided: Serena holds a 7-1 career edge, most recently beating Halep in straight sets at Indian Wells in March. In their only Grand Slam meeting, at Wimbledon in 2011, Serena needed three sets to prevail.

No. 3 Stan Wawrinka vs. Juan Martin del Potro, following Williams-Halep ( Watch)

Although del Potro -- in the midst of yet another comeback from wrist surgery -- is unseeded here, he has beaten the two-time Grand Slam champion in four of six previous matches. Del Potro's most recent victory, a few months ago at Wimbledon, was significant. He won in four sets, and it was the beginning of his confident surge back into the elite level of tennis. Del Potro won this tournament seven years ago, his only major victory to date.