US Open Tennis 2013: Breaking Down Day 9's Biggest Matches

The 2013 U.S. Open is gearing up for the home stretch as the tournament inches toward the quarterfinal round, and competition is only set to get fiercer. 

Despite Roger Federer's untimely exit on Monday, there is no shortage of top-flight players and household names gunning for America's championship, and the action is getting better by the day.

With Day 9 featuring some big-time matchups that will shake up the tournament mightily, let's break down the most exciting upcoming matches for Tuesday.

No. 3 Andy Murray vs. Denis Istomin

The defending U.S. Open champion is cruising toward a potential semifinal matchup with top-seeded Novak Djokovic and will play unranked Denis Istomin of Uzbekistan in Tuesday's fourth-round affair. 

Murray will have to take down a strong family dynamic to make it to the quarterfinal, however. Kevin Mitchell of The Guardian reported that Istomin is actually coached by his mother. 

That likely won't deter Murray from advancing on, but things will get much tougher in the following match. Assuming he gets past Istomin, Murray will face either ninth-seeded Stanislas Wawrinka or No. 5 Tomas Berdych in the quarterfinal.

The Scot can't afford to look ahead, which may be easier said than done given the upcoming slate. If he wants to defend his crown and add to an already successful 2013 campaign, it will take a "one-match- at-a-time" approach from Murray.

No. 9 Stanislas Wawrinka vs. No. 5 Tomas Berdych

Wawrinka has an incredibly rare chance to be a Swiss native not named Roger Federer and seriously contend for a Grand Slam title, but he'll have to get through fifth-seeded Berdych in order to do so.

With a quarterfinal spot on the line, this is the type of matchup that tennis fans crave, as two lesser-known top-10 foes battle for the chance to take on defending champion Murray.

Wawrinka has only dropped one set all tournament, while Berdych has avoided doing so entirely. The Czech native recently beat No. 31 Julien Benneteau 6-0, 6-3, 6-2. 

Berdych will be aiming for his second quarterfinal Grand Slam appearance of the year after making it as far in the Australian Open, but his sights are set much higher after coming within one match of the championship round at this tournament a year ago.

If they can get past one another without wearing themselves out and catch a star on a bad day, either of these players could end up hoisting the men's singles trophy by the end of the tournament. 

No. 1 Serena Williams vs. No. 18 Carla Suarez Navarro 

After getting past a new rival in fellow American and 15th-ranked Sloane Stephens in straight sets, Williams is through to the final-eight contenders and looks poised to win her fifth U.S. Open.

However, she's not quite facing chopped liver in her quarterfinal matchup against No. 18 Carla Suarez Navarro.

Despite not being one of the bigger names on the Grand Slam circuit, the Spanish native is almost a lock to take any formidable opponent to the wire. She proved that against eighth-seeded Angelique Kerber, whom she topped in the fourth round to set up a date with Williams.

Having that much success—or even extending the match to three sets—will be much easier said than done for Navarro, but we've seen crazier things happen. 

Williams should face bigger tests in the semifinal and championship rounds with potential showdowns against No. 5 Li Na and No. 2 Victoria Azarenka, but slip up against Navarro and she could be in big trouble.