The Argentine force had a two-sets-to-love lead and started to feel the emotions and fatigue. His knee was aggravating him, and he was unable to break serve again after the first set came to a close.
Since Delpo came back from a hiatus due to injury he has played Federer six times, losing each and every one of those matches.
The baseline rallies are generally pretty lengthy, and Delpo seems to win a good amount of them, but he continues to fall short of the finish line and was unable to win a set in five straight matches until this past battle.
Besides defeating Roger at the 2009 ATP World Tour Finals and US Open as well as losing twice in five-setters at the French Open, Del Potro has been unsuccessful in taking a set off Fed in all eight of their other encounters. In other words the slower courts (with the exception of Flushing Meadows) suit his game better than Federer's style.
So what is he doing incorrectly? Can he be more successful against the Maestro? And can he win on faster courts against the king of pace?
Surely, his serve is doing him well and is not the biggest problem. But, it is important to note that Roger is treating him the same way he has treated Andy Roddick so often in his prosperous career—once Federer gets the return of serve in play (even a chip or poor slice) his chances of working his way into the point are solid.
Juan needs even more pop on the serve (which he once possessed three years ago), and that may not ever come again. So he should focus more on spot-serving as Fed does—he should try to work the sliders more than the standard heavy, flat ball to Roger's backhand.
Here is why—Roger seems to make more balls in play off his backhand wing than his forehand on the returns, albeit weaker ones. If Delpo can take the forehand weapon away from Roger just for one stroke (the first ball), he can pound the ball to the open court on the deuce-side or to the backhand on the ad-side. This would be much tougher for passing shots and retrievals for him since it is his weaker side, and he would be on the stretch.
Obviously playing strictly to Fed's backhand got Delpo his two huge wins, but times have changed since the wrist injury, and both players have slightly different ground strokes today.
One important factor that is the tell-all is the Argentine's slower wheels today, particularly when running to the forehand.
Because of this he should anticipate more balls to the forehand and not run around so many backhands if he is not permitted enough time to do so.
In return he would develop a stronger backhand and neutralize his opponent's tactics of breaking down one of his shots.
So he can beat Roger and will perhaps perform better in the near future, but as of now he is lacking the proper game plan to beat somebody that can handle pace and give it right back. Not to mention, Federer has variety and spins that Delpo is unaccustomed to seeing from others.
On the faster courts Juan should focus solely on holding serve and hope to take his chances at the latter stages of sets because he sometimes expends too much energy early on and is disappointed when he does not break, which then leads to him losing serve.
He is close to defeating Roger on slow courts, but he must adopt a different approach that isn't so concerned with power and is more centered around strategy and mental focus.
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