By Pritha Sarkar
LONDON (Reuters) - There is a reason why Juan Martin del Potro went under the knife -- over... and over... and over again.
Three wrist operations since his last appearance at Wimbledon in 2013 meant Del Potro had more appointments with surgeons and physiotherapists than on-court engagements with tennis professionals over the past 27 months.
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On Friday, the gentle giant from Argentina showed why all the pain and scars -- both physical and mental -- were worth it as he toppled fourth seed Stan Wawrinka 3-6 6-3 7-6(2) 6-3 under a closed Centre Court roof in the second round of Wimbledon.
"It feels amazing. I beat one of the guys who is playing great tennis this season and I couldn't have expected this before today," a trembling Del Potro said.
"I was really sad for the last two years and now I am enjoying playing tennis again. My hands shaking is a great sensation for me because I'm playing tennis again and I feel alive," he added.
Del Potro, world number 165, was feeling "so alive" that by the time the match hit the mid-way point of the second set, Wawrinka did not know what had hit him.
The Swiss, who won grand slam titles in Melbourne and Paris in the last 2 1/2 years, was probably left wishing Del Potro's surgeon had not done such a good job of fixing the stricken left wrist which he uses to belt his trademark double-handed backhand.
A break for 3-1 was enough for Del Potro to bag the second set and he marked the moment with a clenched-fist salute to his supporters.
While punters on the outside courts had to make do with watching an army of groundstaff dragging the green covers on and off with comical frequency, Del Potro's flowing racket skills lifted the spirits of the soggy fans sitting atop Wimbledon's Henman Hill and following proceedings on the giant TV screen.
By the time the players swapped serves for four successive games at the start of the third set, Wawrinka knew he was in for a torrid afternoon against the 2009 U.S. Open champion.
A forehand long handed the 6-foot-6 Del Potro the third set tiebreak and the Argentine proved his patched-up wrist could go blow-for-blow with Wawrinka's thundering groundstrokes in the fourth as he finished a 21-shot rally with a nerveless volley.
Wawrinka saved two break points in the sixth game, with an ace and a beautiful backhand winner, but his luck ran out two games later as an erratic backhand handed Del Potro the break.
When the Swiss whipped a backhand wide on match point to complete another miserable outing at the only major in which he has yet to reach at least the semi-final, it completed a remarkable comeback from the tennis wilderness for his opponent.
"After my third surgery, I've been trying to play tennis again. It is like my second or third career in my short life," said Del Potro who will next face Lucas Pouille.
"I didn't know if I could be in the top position again... after all the injuries," the 27-year-old added.
"To be in the third round in my first grand slam after three years, it means a lot to me. I'm excited to go far in the tournament."
(Editing by Ed Osmond)