How did Stanislas Wawrinka of Switzerland find the zone down 2 sets to 1 and 1-3 in the fourth? Gilles Simon of France was riding the home crowd energy and pushing toward the finish line. However, Wawrinka found another gear and eventually won the match going away in the fifth set.
For much of this match Wawrinka dictated the outcome of the points having far more winners and unforced errors (in fact 82 winners to Simon's 23, and 88 unforced errors to Simon's 49). Gilles Simon attempted to play more aggressive and finish points by coming forward, but the "easy power" of Wawrinka allowed him to control the court. In particular his backhand down the line punished Simon time and time again.
Thus the issue for Simon in this match; he did not have the weapons to dictate against a powerful baseliner Wawrinka. Despite this, Simon was able to gain the lead and seemed on the way to victory playing very solid, consistent tennis. This game plan worked until Wawrinka stopped making errors, became more consistent, and hit a flurry of winners. In the fourth and fifth sets Wawrinka flipped his winners to unforced errors ratio; he had 28 winners and 21 unforced errors.
The question still remains, how did Wawrinka get into the zone after nearly 3.5 hours of tennis? First, Wawrinka must be in tremendous condition. Simon forced Wawrinka into long rallies throughout the match including grueling Sets 1-2 that took over 2 hours. Wawrinka continued to move his feet and get in to position to strike the ball late in the match even though he expended tremendous effort in the sets prior.
Second, Wawrinka was able to find the zone because Simon was playing great tennis and gave Wawrinka a chance to elevate his game. Simon is not going to hit you off the court; hitting winners is not his game. This gave Wawrinka a ton of looks at the ball, he got into a superb rhythm, and he was able to maintain that for the last nearly hour of the match. The zone or flow state can be achieved when the challenge is optimal. Wawrinka was challenged, but not so much that would cause a decrement in his play. That is a problem when you play his countryman Roger Federer . Fed is not going to give you that many looks to get into a rhythm.
A third reason I would speculate that Wawrinka found the zone in the fifth set when most players would have been just trying to hold on physically, mentally, emotionally - Wawrinka was composed and did not waste extra energy throughout the match with emotional outbursts, fights with the officials, or yelling at himself. Wawrinka, even though his play was a little bit of a rollercoaster, did not allow his emotions to take him on a rollercoaster ride. In doing so, Wawrinka was in a good mindset despite being down 1-3 in the fourth. He still believed he could win. He just had to start making more balls, something he controls. And, like I wrote before, Simon was not going to hurt him too much so Wawrinka knew the match was on his racket. Wawrinka's emotional toughness allowed him the opportunity to find his "A" game in the most intense situation.
In the round of 16 Wawrinka will have a rematch from last year's French against Tsonga. Wawrinka was down 2 sets to 1 in that match as well. He will have great belief he can win this match. If he plays like he did the last hour of his third round match the rabid French fans will likely be disappointed again.