Juan Martin del Potro was already the feel-good story of the 2016 men's tennis year before this weekend's thunderclap ending in Zagreb, Croatia. But his titanic comeback Sunday that sent Argentina winging to its first Davis Cup title just made his year seem more monumental -- and emotional -- and sparked new dreams of how he could stir up the mix in 2017.

The sight of Del Potro standing on court, arms outstretched and head thrown back, soaking in the chants and love of the 1,500 or so Argentine fans who had traveled halfway around the world to see it, was the sort of moment he wasn't sure he would ever get to experience. But it was a beautifully fitting 2016 curtain call for one of the most popular but star-crossed men in tennis. It's hard to exaggerate how hard and despair-filled his climb back has been.

Del Potro was only 20 when he beat Rafael Nadal in the semifinals and then Roger Federer in the final to win the 2009 U.S. Open, snapping Federer's title string at five. No one else had ever beaten those two back-to-back in a Slam by then, and big things seem guaranteed for Del Potro. He already stood 6-foot-6; he could blast the ball off either wing and yet move like a much smaller man. But starting the very next year, Del Potro endured three wrist surgeries and sometimes doubted he would ever play on tour again, let alone find himself standing there Sunday after rallying from a two-sets-to-love deficit for the first time in his career to beat Marin Cilic, and spark Argentina's last-day comeback against Croatia.

Federico Delbonis, primarily a clay-courter, finished it off with an assured win against Ivo Karlovic, a man ranked 20 places higher than him, and Del Potro joined the Argentine team as it sprinted out to mob Delbonis on the court afterward, and then hoist the trophy as confetti rained down.

It was Argentina's first win in five trips to the Davis Cup final, and Del Potro, who had been a part of two of those previous losses, was so overcome he admitted it was hard for him to speak.

"Thanks to all those who prevented me from retiring," he said. "I was very close to never playing again, and, well, here I am."

Del Potro, now 28, had played only 14 matches in all of 2014 and '15, when he started this latest comeback at a small-scale tournament in Delray Beach, Florida, in February. His world ranking had plummeted to 1,042, and the early scouting reports were downbeat. Del Potro still had his sledgehammer forehand, and his serve was fine. But his backhand was a whisper of what it was, and no one knew when -- or if -- it would come back enough. Least of all him.

Juan Martin del Potro helped Argentina win its first Davis Cup final on Sunday. Reuters/Marko Djurica

"I don't know if I can be in the top positions again," he said at one point this summer. "But if not, I will be happy just to be playing tennis again."

But Del Potro adjusted -- "He's a genius, [and] his heart is so big," Argentina Davis Cup captain Daniel Orsanic said Sunday -- and his year really began to take off after he upset Stan Wawrinka in the second round at Wimbledon. He seemed to fall upon something strategic then: using his low-slice backhand as a tempo-changing complement to his booming forehand.

From there, it was on to the Rio Olympics, where Del Potro upset top-ranked Novak Djokovic in the first round, reducing the Serb star to tears. Then he knocked off Nadal in their semifinal match.

Though Andy Murray -- now the world No. 1 -- beat Del Potro in a four-hour final for the gold medal, Del Potro was again heartened. Playing as a wild-card entry in the U.S. Open a few weeks later, Del Potro roared to the quarterfinals and broke down crying when fans there surprised him by spontaneously serenading him with chants of "Delpo" in the wee hours of the morning, even though Wawrinka was about to avenge his Wimbledon loss by serving out their match.

Del Potro had another breakthrough when he won his first title in 33 months by beating Jack Sock at the Stockholm Open in October.

Then, faced with beating Murray again -- this time at last month's Davis Cup semifinals in London -- he clawed out a five-set thriller in 5 hours and 7 minutes, the longest match either of them had ever played, to end Britain's reign as Davis Cup champs.

That win, like Sunday's team victory against Croatia, was the sort of unprecedented stuff that was predicted for Del Potro when he was a younger man. His honesty about all the doubts surrounding his career and his tears of appreciation sandwiched between those bookend moments of his career -- his 2009 U.S. Open win and Sunday -- has only endeared him to his fellow players and fans even more.

It's easy to understand why. There is always something riveting about seeing someone whose life exceeds their dreams.

No matter what happens from here, Juan Martin del Potro just forever became one of those athletes. He has now climbed to the summit of his sport twice. And part of what dignifies him is the shift in perspective and gratitude that has come with it.

"I'm just so happy to be playing again," Del Potro said Sunday, again through tears. "This kind of moment is what I was missing."