WIMBLEDON -- Three hours before Friday's Centre Court match, Juan Martin del Potro strolled through the deserted grounds.
On his way to the practice courts, the 6-foot-6 Argentine laughed with two members of his team, waggling his plastic-wrapped racket with his left hand.
He didn't seem to have a care in the world. In truth, no current player with his extraordinary skill set has suffered more heartache as a result of his own fragile body.
Since winning the US Open seven years ago, del Potro has endured no fewer than four surgeries on his left and right wrists. It has been three years since he last played here, reaching the 2013 semifinals at the All England Club.
"I'm enjoying tennis again," del Potro said after winning his first match earlier this week. "I'm starting to talk about tennis and no more about my wrist. That's important."
Incredibly, with very little ramp-up, del Potro's wrist and tennis are both officially top-10 ready. He scorched/stunned/slammed No. 4 seed Stan Wawrinka 3-6, 6-3, 7-6 (2), 6-3 to advance to the third round. Wawrinka is the highest seed to exit the men's tournament thus far.
To say he is ahead of schedule would be a gross understatement.
Del Potro's hands were still shaking when he stepped off the court and into the BBC interview area. He called it his most emotional victory ever.
"It feels amazing sensation for me at the moment," del Potro said with feeling. "I beat one of the guys who's playing great tennis. I couldn't expect this victory today. I am very, very happy."
It was a delicious and uncommon second-round matchup between two former Grand Slam champions, given del Potro's layoff-induced ATP ranking of No. 165. While Roger Federer, Rafael Nadal and Novak Djokovic have monopolized the majors, winning 43 singles titles, these are two of the other four active players to experience a Slam victory.
Del Potro's formidable right-handed forehand -- the one that unstrung Federer in that 2009 US Open final -- can still be, quite literally, breathtaking. In a first-round match against Stephane Robert, del Potro's first Grand Slam appearance in 29 months, it sometimes drew gasps from the knowledgeable crowd on Court 12.
Del Potro's flat, two-handed backhand was once one of the game's best. Now, it is a ghost, a drastically reduced one-handed shot that is invariably sliced. There are times when, under duress, he instinctively uses both hands, but you can feel his hesitation, his fear of a relapse.
"I'm not having all my confidence on my backhands yet," he allowed. "And that's tough when you play against the top guys because they are so good players and they are strong enough to play in the fifth set matches. I'm expecting be better in the future, but for this year, my biggest challenge could be finish healthy and ready to make a good preparation for the next year."
Against Wawrinka, del Potro's serve and the forehand were in vintage form. Forty percent of del Potro's serves were unreturnable. His fastest serve: 135 mph. In two matches, he has hit 26 forehand winners -- against only one on the backhand side.
"As we all said, it's great for the tennis to see him back," a disconsolate Wawrinka said in his postmatch news conference. "You see already, he beat some good players. His backhand is still struggling because he cannot play completely, but on this grass the slice is still difficult."
In the first set, he squandered two break-point opportunities but converted one of two in the second. In the third, he played a pristine tiebreaker, while Wawrinka melted down, throwing in a double fault and a bad forehand error at the end.
"After my third surgery, I was really sad, sitting at home," del Potro said. "This is like my second or third career in my life, and now I am enjoying. It's a great sensation for me, and I feel alive."
"I could not expect to be in third round of Wimbledon after three years. And now to the end [of the tournament], everything is very positive. I am in a good way to be[ing] 100 percent."
Del Potro slipped and fell near the end of the first set and stayed down along the baseline for a minute or so. Slowly unspooling his long body, he gingerly got to his feet. That's how most people thought it was going to be this year for del Potro.
Rather, this result is a bolt of lightning for men's tennis. If he can beat a two-time major champion with one hand tied behind his back, what will he do with two healthy hands?
At 27, del Potro is still relatively young; Wawrinka won his first Grand Slam, the 2014 Australian Open, two months shy of his 29th birthday and his second, last year's French Open, at 30.
For now, he will continue to fight the urge to be aggressive.
"I believe on myself, I believe on my wrist," del Potro said. "I would like to get better faster than I'm doing now, but that could be dangerous for my body. I'm working hard mentally, too, because I have to deal with some pains and some frustrations when I want to hit a good backhands and I cannot do it.
"I hope to be ready for being aggressive player on next season."