Nadal shines, Federer fades as big four becomes three in 2013
Spain's Rafael Nadal celebrates beating Switzerland's Stanislas Wawrinka during their group A singles match in the round robin stage on the third day of the ATP World Tour Finals in London on November 6, 2013
Nadal was sport's comeback man of the year, collecting 10 titles from 14 finals, including a landmark eighth French Open, a second US Open which took his career majors tally to 13, and a record 26th Masters.
He ended the season with 75 wins against just seven losses and another $14.5 million banked to take his career earnings past the $60 million mark.
It was a rebirth that got off to a faltering start when the Spaniard, who had been out of action for seven months, reappeared at the modest Chilean venue of Vina del Mar in February.
His run to the final was ended by Horacio Zeballos, ensuring the journeyman Argentine a rare mention in despatches.
But from then on, Rafa was rolling.
He swept to Masters titles in Indian Wells, Madrid and Rome with his defeat in the final of the Monte Carlo Masters at the hands of Djokovic, which denied him a ninth successive triumph in the principality, an unexpected blip.
The 27-year-old then beat compatriot David Ferrer in the final of the French Open to become the first man to win eight Roland Garros crowns.
On the way to another Paris triumph, he had stared down Djokovic in a classic semi-final duel, fighting back from 2-4 down in the deciding set.
Nadal's bittersweet relationship with Wimbledon took another twist two weeks later when the 2008 and 2010 champion crashed to defeat on the first day to Steve Darcis, the world 135 from Belgium.
Was that a sign all the old physical frailties were about to conspire once again against him?
Not really. He took a time-out, headed off to North America, captured the Masters in Montreal and Cincinnati before claiming his second US Open title with a four-set win over Djokovic.
By November, Nadal had wrapped-up the year-ending world number one spot for a third time.
"It's very special what happened this year. For me, the emotions of this year after a tough time have been fantastic," said Nadal, shrugging off his ATP World Tour Finals loss to Djokovic in London.
Djokovic started 2013 with a fourth Australian Open title, then lost the Wimbledon final to a history-making Murray and the US Open championship match to Nadal.
He ended it as ATP World Tour Finals champion on a 24-match winning streak and announced he would be marrying long-time girlfriend Jelena Ristic.
Four of the Serb's seven titles in 2013 came in the season's closing weeks, although defeat in the Davis Cup final at the hands of the Czech Republic darkened the mood.
Murray missed the latter part of the season after undergoing surgery on a long-standing back problem in September.
But by then his work was done.
On an emotional July afternoon, the 26-year-old brushed aside an under-powered Djokovic to become the first British man to win Wimbledon since Fred Perry in 1936.
Murray credited coach Ivan Lendl with his success, a second Grand Slam title to add to his breakthrough 2012 win in New York.
"He believed in me when a lot of people didn't," said Murray.
It was a year to forget for Federer, the record-setting 17-time major winner whose decline appears to be irreversible.
He failed to reach a Grand Slam final for the first time since 2002 and won only a solitary title in Halle as his ranking slumped to seventh in the world -- his lowest placing for 11 years.
His second round defeat at Wimbledon at the hands of Sergiy Stakhovsky, the world number 116, was his worst defeat at the All England Club in 11 years and ended his run of 36 consecutive Grand Slam quarter-final appearances.
The 32-year-old then suffered his earliest US Open exit for a decade when Tommy Robredo, who had lost all 10 previous meetings with him, beat him in straight sets in the fourth round.
But the Swiss star, who ended the season at six in the world, has no intention of quitting.
"This is what I used to do as a little boy. It's something that always is there in your DNA," Federer said.
The year also witnessed a series of epic encounters.
The pick was Djokovic's five-hour win over Stanislas Wawrinka in the Australian Open fourth round which was achieved 12-10 in the final set after the Swiss, one of 2013's most improved players, had raced to a 6-1, 5-2 lead.
Doping issues proved a headache with Viktor Troicki and Marin Cilic handed suspensions.
Troicki is serving a 12-month ban for failing to supply a blood sample on demand at the Monte Carlo Masters in April when he claimed he was too ill while Cilic served a four-month suspension after testing for banned stimulant nikethamide at the Munich Open in May.