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When a then-20-year-old Juan Martin del Potro blasted his way past Rafael Nadal and Roger Federer to win the 2009 U.S. Open, it looked as if a new force had arrived.

The 6’6” Argentine possessed remarkable agility and lateral quickness for his size, becoming far more than just a brute slugger. But could he ever pulverize the ball. With his lethal forehand, Del Potro had the ability to hit people off the court and dictate matches from the baseline. His blistering groundstrokes often proved unreturnable for even the best defenders.

Against five-time defending champion Federer in that U.S. Open final, Del Potro’s bruising style put his opponent on the ropes, and he delivered the knockout punch in a dominating fifth set.

That victory served as his breakthrough moment, and projecting him to win several more Grand Slam titles didn’t seem all that far-fetched.

And then fate struck him down.

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Del Potro’s upward trajectory came to a screeching halt a few months later. After suffering a right wrist injury in January, he underwent surgery and missed the rest of 2010. With just six matches under his belt that season, his ranking plummeted.

He’d return at the start of 2011, but Del Potro never really found his rhythm that year, winning just two small events and not making any serious noise at the Grand Slams. Chalk that up to rust from so much time on the shelf.

The next year was a much different story, as a resurgent Del Potro won bronze at the 2012 Olympic Games, reached three major quarterfinals, captured four titles and finished inside the Top 10. That momentum carried over into 2013, when he made the Wimbledon semifinals on his way to a year-end rank of No. 5.

During those two successful seasons, Del Potro re-established his place among the elite. He inched closer and closer to taking home another Grand Slam victory.

Sadly, the injury bug bit him early in 2014, and he's played only 14 matches since then. The culprit? Another wrist injury, this time to his left one. Though he tried seeking other means of treatment, Del Potro couldn't escape a trip under the knife.

Two more surgeries followed in 2015, as Del Potro struggled with hitting two-handed backhands while training. His decision to return to the operating table a third time was a necessary one in order to finally become pain-free in his left wrist.

Afterward, Del Potro shared his thoughts in an emotional Facebook post:

The hardest moments of my career are gone, those in which I didn't know what I would do next. I've already told you the discomfort of being unable to do what I like and the suffering of watching tennis on TV. Today is a different story. I have great expectations for a new stage that began this week. Today I am more committed than ever to trying to come back. No more doubts or question marks. A new career for me starts today.

But as he returned to the sidelines for another extended period and began more rehab, it became easy for outsiders to wonder if Del Potro would ever play again. It's rare to see an athlete lose two-straight years in their prime and pick up where they left off.

He wouldn't wave the white flag, however, and vowed to make it back.

In a video recently posted to his YouTube page, Del Potro announced he would return at this month's Delray Beach Open.

"The uncertainty. All the bad moments I had to go through. So many mood swings, really difficult days that make you think about giving up," Del Potro said in the message.

Clearly, being away from the game for so long tortured him inside. Instead of succumbing to those doubts and insecurities, he persevered with the help of his team. That experience only strengthened his resolve.

Now that Del Potro is ready to give things another go after a few short-lived returns, here's hoping he stays on the court for good.

At age 27 and in an era when players are competing well into their 30s, time is still on Del Potro's side. If his body holds up and he can avoid any more serious injuries (a big "if"), the Argentine could have several more productive seasons.

While he'll try to ease into form throughout 2016, Del Potro has nowhere to go in the rankings but up. He sits at No. 1,045, a far cry from his days as a Top 10 mainstay. Slowly but surely, he'll rise again.

And his inspiring return should inject some new energy into men's tennis and possibly shake up the dynamic at the top of the game.

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At his peak, Del Potro could strike fear into any opponent. He was one player who repeatedly made Novak Djokovic sweat, with their epic 2013 Wimbledon semifinal one of the sport's all-time great matches. Maybe he can become a challenger to the world No. 1 once again.

Del Potro also racked up quite a few wins against the other Big Four members (Federer, Nadal and Andy Murray) over the years. His intimidating game translated well to all surfaces and situations, resulting in 18 titles between June 2008 and January 2014. Against Federer, it's notable that he holds a 4-0 advantage in finals. That is quite an impressive feat.

Because of his considerable skill as well as a friendly demeanor, Del Potro fosters a ton of respect from his peers. As Federer told Tennis.com's Matt Cronin last year: "It's been rough to see him go under the knife so many times now, not be around really. I've always enjoyed the matches against him. He's one of the best ball strikers we've ever had in the game."

In his absence, men's tennis has missed one of its best competitors. He forced other foes to go outside of their comfort zones to adapt to his power. Had he been healthy the last two years, it's reasonable to assume Del Potro would have challenged Djokovic and Federer for some of the important titles.

The former U.S. Open champion's comeback therefore introduces another variable for Djokovic and the other top contenders to keep an eye on. That possibility should excite fans.

Not content to end up as a "what if" tale, Del Potro has a new lease on his tennis life and is determined to make the most of the opportunity. Let the second act begin.

All statistics are courtesy of ATPWorldTour.com unless otherwise noted.

Joe Kennard is a featured columnist for Bleacher Report.

Follow @JoeKennard