WHAT HAPPENED: No. 5 seed Stan Wawrinka advanced to the fourth round on Saturday with an at times shaky performance, winning in straight sets over Ruben Bemelmans of Belgium, 6-3, 7-6, 6-4.
Wawrinka has yet to drop a set in the tournament but has managed to raise doubts about the state of his game. Yet to face a seeded player, Wawrinka will next take on No. 68-ranked Donald Young, a winner over No. 22 seed Viktor Troicki earlier in the day.

Of particular concern of late has been Wawrinka’s serve, and it was off again today. He had eight double faults and connected on just 45 percent of his first serves. 

Wawrinka didn’t seem to truly get fired up in this match until he was serving in the third game of the second set and missed an easy backhand into the bottom of the net, and then double faulted to go down, 15-40. At that point, he smashed a ball into the stands, smashed his racquet, gave the mangled racquet to a thrilled fan and then proceeded to reel off the next four points, suddenly grunting and digging out every ball. 

Wawrinka’s new energy was short lived, however, and he lost his serve in the fifth game, Bemelmans taking advantage of a weak, 89 mph second serve and nailing a backhand return winner up the line for the break. 

Bemelmans played valiantly throughout, particularly considering the stature of his opponent and the packed house in Louis Armstrong Stadium. Prior to this US Open, the Belgian had won just one Grand Slam match, at Wimbledon in 2012, and had lost in the qualifying of the US Open every year between 2009 and 2014.

Serving at 4-5 in the second, Bemelmans saved two set points. But in the tiebreak, the Belgian made four unforced errors off return of serves, helping Wawrinka take the breaker, 7-5.

Wawrinka raced to a 5-2 lead in the third and managed to hold on after getting broken in the eighth game and facing two break points when serving for the match again at 5-4. 

WHAT IT MEANS: With the win, Wawrinka has now reached at least the fourth round here for the fourth time in a row. He has reached the quarterfinals or better in seven of the past eight Grand Slams, including victories at the 2014 Australian Open and this year’s Roland Garros. Yet, he certainly hasn't been in top form yet in New York. Perhaps it has to do with the fact that, in the summer hard court season, he played just four matches, withdrawing from his first-round encounter in Montreal citing a back injury. Only time will tell if the Swiss No. 2 player will find the form that has propelled him to the level of his recent success. 
QUESTION: Wawrinka's next opponent, Donald Young, is playing inspired tennis right now and will likely have the American crowd solidly behind him when they meet. Does Wawrinka need to be worried? 
September 3, 2015 - Stan Wawrinka in action during a men's singles second round match at the 2015 US Open at the USTA Billie Jean King National Tennis Center in Flushing, NY. (USTA/Steve Ryan)