Fifteen months after Federer became the sixth man in history to win all four Grand Slam titles, Nadal became the seventh in 2010 when he won the U.S. Open, his third major in a row after the French Open and Wimbledon.
During a dominant season, the 24-year-old Spaniard wrested back the No. 1 ranking from Federer, and racked up seven titles, including a record-breaking 18th Masters Series win. With an Olympic singles gold and two Davis Cup titles already in the bag, Nadal is fast running out of major prizes to win.
"It has been an incredible season," Nadal said. "One of my best ever, if not the best."
In an average season by his very high standards, Federer saw his streak of 23 Grand Slam semifinals ended by Robin Soderling at the French Open. He also fell in the quarterfinals to Tomas Berdych at Wimbledon, and then lost an epic semifinal match at the U.S. Open despite holding two match points against Novak Djokovic.
Federer still managed to pick up the other two significant titles of the year at the Australian Open and ATP World Tour Finals, the latter with a series of dominant performances that hinted he is not quite ready to fade into the background.
Since 2004, Federer and Nadal have won 24 of the 28 Grand Slam titles and with the pair cleaning up again, there was a sense of familiarity - perhaps even staleness - about 2010.
Just as in 2009, Djokovic and Andy Murray lined up third and fourth in the rankings. Juan Martin del Potro, the winner of the 2009 U.S. Open and the emerging star of that season, spent most of 2010 recovering from wrist surgery and ended it ranked No. 257.
Djokovic may not lose any sleep over not adding to his lone Grand Slam win after he led Serbia to its first ever Davis Cup victory, beating France in the final. He described it as "our biggest success as individuals, as a team, as a country." Italy, meanwhile, won the Fed Cup for the third time in five years, beating the United States in the final.
In the men's year-end rankings, there were no teenagers in the top 100 and the only players to finish in the top 20 for the first time were Jurgen Melzer (age 29), Mardy Fish (29), Sam Querrey (23) and John Isner (25).
That was far from Isner's most memorable contribution to the year. That unraveled over 11 hours, 5 minutes at Wimbledon as he and French opponent Nicolas Mahut played the longest match in history over three days, with the American eventually winning 70-68 in the fifth set.
"It stinks someone had to lose," Isner said of an extraordinary match which captured the public's imagination to such an extent that it even overshadowed Queen Elizabeth II's first visit to Wimbledon in 23 years.
Isner took significantly longer in beating Mahut than Serena Williams did in defeating all seven of her opponents on the way to a fourth Wimbledon title.
But Serena, who also won the Australian Open, did not end the year as No. 1. Nor did Kim Clijsters, the U.S. Open champion and winner of the year-end championship.
That honor went to Caroline Wozniacki, a 20-year-old Dane who didn't reach a Grand Slam final in 2010 but picked up a tour-leading six titles while her rivals fell away.
Serena has not played since stepping on some broken glass at a restaurant and tearing a tendon in her foot shortly after winning Wimbledon. Justine Henin's comeback after a 16-month retirement ended at the same tournament when she hurt her elbow.
Venus Williams managed just one more tournament after Wimbledon - the U.S. Open. Clijsters continues to pick and choose her tournaments around her family life. Jelena Jankovic won a total of four matches from August onward. Elena Dementieva, a two-time Grand Slam finalist and former No. 3, retired altogether.
The state of flux in women's tennis at least allowed Francesca Schiavone to provide the feel-good story of the year by winning her first Grand Slam title at the French Open at the age of 29 - at her 39th major.
"This means that everybody has the chance to be who really you want to be, and to do everything in your life," Schiavone said. "This is what happened to me."
Next year could produce some comebacks in women's tennis: Venus, Serena and Henin should return from injuries, while Maria Sharapova and Ana Ivanovic showed signs in 2010 that they might be regaining their lost confidence.
And while Wozniacki will be desperate to back up her top ranking with one of the sport's major titles, Nadal can hold all four Grand Slam titles at the same time by winning the Australian Open in January - an achievement that has so far eluded Federer.
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