The latest edition of this series on notable Americans in 2013 focuses on the top-ranked American man, who alternated between stunning peaks and dismal valleys. 

John Isner entered the 2013 campaign full of promise with his sights aimed squarely on breaking into the upper tier of the ATP. But, in what has become a recurring theme of late, an assortment of injuries fell in the path of the top American.

The 28-year-old had finished a busy 2012 season with a ranking of world No. 14 and had shown signs of breaking down barriers that had previously prevented him from qualifying for the ATP World Tour Finals. His ability to defeat top-10 players had become more commonplace with victories against the likes of Roger Federer, Tomas Berdych and Jo-Wilfred Tsonga last year.

Nevertheless, the momentum that Isner gained last season took a quick turn in the opposite direction in his first match of 2013, when he fell in straight sets to Ryan Harrison at Sydney. Isner subsequently withdrew from the Australian Open due to a bone bruise on his knee, an injury that would linger for much of the first half of the season. He chose to nurse his knee without leaving the friendly confines of his home turf, playing exclusively in the United States until mid-April.

During this stretch, Isner won the first of his two titles in 2013, defeating Nicolas Almagro at the US Clay Court Championships in Houston. Turning his attention to Europe, he did not find the same success on the clay across the Atlantic. Isner won just six total matches in five clay tournaments there, including a third-round defeat at Roland Garros. Those struggles did not depart from the usual pattern of top American men, though, for champions such as Andy Roddick rarely achieved much on that surface.

Isner's injury woes deepened when he was forced to withdraw with an injury to his quadriceps tendon in the second round at Wimbledon, just two games into his match with Adrian Mannarino. Hoping to turn around a disappointing season, the American turned to a place that had witnessed much of his earlier success: the US Open Series. Always at his best on home soil, the former University of Georgia star immediately saw results with a semifinal on grass in Newport and built on that encouraging week by winning his second title of the season in Atlanta.

Finally, it appeared the frustration of the first two-thirds of the season had lifted after those two performances. Isner also advanced to the final of the ATP 500 tournament in Washington, falling to Juan Martin Del Potro. But his best performance of the season still lay ahead.

At the Masters 1000 tournament in Cincinnati, Isner not only obtained revenge for his loss to Del Potro but defeated rising star Milos Raonic and served notice that he was back with a stunning victory over world No. 1 Novak Djokovic. Only year-end No. 1 Rafael Nadal could stop the American in a two-tiebreak final, just weeks before Nadal would lift the trophy at the US Open.

Isner had injured his ankle early in that stellar week, however, and he withdrew from his home tournament in Winston-Salem, North Carolina in an effort to get healthy for the US Open. Unfortunately, his effort to regain his health proved futile. Isner’s stay in Flushing Meadows was short, ending with a loss to Philipp Kohlschreiber in the third round. After using home venues in the United States to regain momentum earlier in the season, Isner found no solace on his country's biggest stage.

The frustrations of an uneven, injury-strewn campaign may have come to a head after his victory over Gael Monfils in the second round of the US Open. During that match, fans cheered boisterously for the Frenchman against Isner. Feeling betrayed by the crowd at his home major, Isner lashed out afterward.

“I was a little bit disappointed in that, actually,” said the top-ranked American man. “Not going to sugarcoat it. If I was playing him in France, it certainly wouldn’t be like that.”

Isner finished 2013 without making a serious charge at any other tournament. However, despite the inability to gain traction due to various injuries, he was able to maintain his ranking and finished the season where he started it at world No. 14.

Additionally, despite success in the last few years, some still unfairly associate Isner only with his 2010 Wimbledon match against Nicolas Mahut, which finished 70-68 in the fifth set as the longest match in tennis history. Isner once said that he is determined to escape the shadow of that match. Success at majors would go a long way in doing just that. To date, however, his best performance at a major remains his 2011 US Open quarterfinals appearance. This season, injuries hampered Isner from improving on previous results at majors, thus failing to further establish an identity distancing himself from that tag.

But positive takeaways still emerge from this season plagued by injuries. Despite setbacks, the big-serving Isner won two titles, maintained a top-15 ranking and showed how dangerous he is to the best in the world when healthy. At 28 years old, and entering 2014 healthy, his goal for the upcoming season should be similar to his goals for this season.

Qualifying for the World Tour Finals and deep runs at majors should lie at the top of his to-do list. Those goals are certainly not an implausible objective, considering what he has shown us so far.