KEY BISCAYNE, Fla. -- The shadows had already encroached on most of the purple center court here early Sunday evening when Juan Martin del Potro formally announced his return to Grand Slam-level tennis.
Robin Soderling, the No. 4-ranked player in the world, had pinned the 22-year-old Argentine deep into the corner and forced a defensive backhand. Soderling whipped another heavy forehand, cross court, and the point appeared to be over. Del Potro, closing ground with the impossibly long strides his 6-foot-6 frame allows, not only got to the ball, but he crushed a running forehand past a startled Soderling.
Del Potro, perhaps aware of the significance, admired the shot for a bit longer than necessary, then raised his right fist -- or was he showcasing his new-and-improved wrist? -- and turned to his box. Five seconds later, with the first set now his, that fist was still up there.
It was the decisive stroke of the match -- perhaps even of the long, nervous comeback from serious wrist surgery -- and del Potro ultimately would prevail in a 6-3, 6-2 smackdown that was over in 76 minutes. It was his first victory against a top-10 player in 16 months; he beat Soderling, then No. 9, at the year-end ATP World Tour finals in 2009 before falling to Nikolay Davydenko.
Even before it happened, del Potro had downplayed the significance, saying, "I think I have a difference between me and Rafa or top 10 players at this moment, but is getting closer."
"I am not thinking about that," del Potro said in his soft, thoughtful way. "I am just doing my road. It's a long road to come to the top again. I'm working hard every day. I'm improving very slowly, taking it match by match. I'm trying to be calm. Maybe for the second half of the year I'll be ready to play with the top players."
Del Potro answered that question in English, but when it was time for Spanish, he was engulfed by the biggest postmatch interview crowd so far at this event. There are 43 credentialed media from Argentina, and more than half of them were in the Sony Ericsson press room. For them, del Potro is again a major story.
It wasn't as if the tennis world hadn't seen del Potro coming; he was No. 6 in the world at the tender age of 20, when he reached the finals of the 2009 U.S. Open. Federer had won five straight titles in New York, but in a sequence of events reminiscent of Marat Safin-Pete Sampras nine years earlier, Del Potro put the hammer down in the fifth set. The way del Potro hit that slingshot forehand past Federer, you would have sworn an era was over -- and a new one was beginning.
But the stress on that fabulous fulcrum proved too much. Del Potro played only three matches in 2010 and missed eight months following surgery. His comeback this season has been understandably tentative.
He split his first four matches In Sydney and Melbourne, before reaching the semifinals in San Jose and Memphis. He won a week later in Delray Beach and you could see the confidence rising in the pace of that forehand. He lost to Nadal 6-4, 6-4 in the Indian Wells semifinals and there was a growing sense he was ready for some big-boy tennis.
Against Soderling, del Potro's serve was ridiculous. He hit 11 aces and allowed the Swede zero break points. He also played the kind of scuffling defense that distinguishes him from some of the other tall, big hitters. Three of his last four serves were utterly unreturnable.
"Today my serve worked incredibly," del Potro allowed.
Soderling, who was under the weather in a second-round loss at Indian Wells, never looked comfortable, as his 25 unforced errors suggest. The player who started the season 18-1 with three titles has cooled off considerably.
Afterward, Soderling was asked if we had seen the old del Potro, circa 2009. He didn't sound completely sold.
"Well, I don't know," Soderling said. "I haven't seen him play since his comeback. I'm not sure. You know, obviously he's playing well. I wish I could have played a little bit better."
"The first thing that comes to mind is probably underdog, which is probably what I'll be," said Fish, whose ranking of No. 15 is 36 spots higher than del Potro's. "Juan seems to be back to his normal self."
Which means the Big Three may soon be adding one more to their golf foursome.
Greg Garber is a senior writer for ESPN.com.