2017 was the year when tennis went back to the future. For the first time ever Roger Federer and Rafael Nadal picked up two grand slam titles each, and the thrilling Australian Open final between the two evergreen legends was a reminder of why the match-up is viewed by most observers as the greatest rivalry in tennis, and possibly even in all of sport.
The pair have taken tennis to new heights and over 13 years have lifted the other's game to levels never seen before in the game.
Federer has more slams than any male player in the history of the sport with 19, while Nadal is in second place with 16. The Spaniard though leads the overall head to head 23-15 and has won nine of the pair's 12 grand slam matches.
Ahead of the Australian Open getting under way next week and with the pair seeded No 1 and No 2, Telegraph Sport breaks down their rivalry into five chapters.
Federer vs Nadal: ranking their greatest ever grand slam matches
2004-2006: The master and the young pretender
By the time Federer and Nadal first met it was March 2004 and Federer, aged 22, was already a multiple grand slam champion. Nadal by contrast was just 17 and taking his first tentative steps in the sport. Still, the young Spaniard won the match 6-3, 6-3 in Miami and people were beginning to take notice of the wild-haired youngster with the long shorts and singlet.
Just over a year later the pair met in a grand slam for the first time, and it was Nadal, on his 19th birthday, who claimed the victory in a four-set French Open semi-final. Nadal went on to win the title two days later, and well and truly announce himself as a potential rival to the great Swiss, who ended 2005 with six slam titles.
By the end of 2006, the two players had settled into a bit of a pattern. Federer would win pretty much all of the high-profile grass and hard-court titles, and Nadal would hoover up anything on clay. When they faced each other, it tended to be Nadal who come out on top, winning three clay-court finals that year - including the French Open - but losing the Wimbledon final in four sets.
Despite losing at SW19 though, the tournament was something of a breakthrough for Nadal, who reached his first Wimbledon final having never advanced further than the third round. The Spaniard was starting to believe that he could play on the grass, despite being written off by most as a clay-court only specialist.
Federer wins: 3
Nadal wins: 6
Federer grand slams: 8 (he also won one in 2003)
Nadal grand slams: 2
2007-2009: The blazer and the pirate
These were truly halcyon days for the sport when Federer and Nadal's rivalry reached its apogee and took the tennis world's breath away.
By the start of 2007 Federer and Nadal were ensconced as the world's No 1 and 2, having finished each of the previous two years in that spot (and 2004 at No 1 in Federer's case). The pair would end up finishing every year as one and two between 2005 and 2010, which is a record sequence in the history of the ATP rankings.
They were so dominant that they contested five grand slam finals between 2007 and 2009, with Nadal winning four of them. Each final was significant for different reasons, with Nadal's 6-1, 6-3, 6-0 evsiceration of his rival at Roland Garros in 2008 the most one-sided final between the two, as the snarling Spaniard clung on to the French Open title with the ferocity of a guard dog protecting his house from unwanted intruders.
The 2009 Australian Open final and 2007 Wimbledon finals were also memorable and hard-fought five-setters, with Nadal taking the former and Federer the latter.
But the peak of the rivalry, and surely of tennis as a whole, came on Sunday July 6 2008. Federer bestrode the Centre Court like a colossus, wearing his personalised cardigan having worn a monogrammed white blazer the year before at a venue where he had won five straight titles. Nadal entered in his three-quarter length shorts and vest, looking like a swashbuckling pirate hungry for booty.
Everything had come down to this - Nadal had inflicted four straight defeats on Federer at the French Open but this was Wimbledon, this was Federer's territory. What ensued was the single greatest match in the history of the sport, with Nadal eventually triumphing in five sets at 9.15pm local time after 4 hours and 48 minutes of play as the two titans of the sport finished the match in almost darkness.
The King had been dethroned at last.
But though the final represented a high watermark for the sport, it did not instantly herald an era of dominance for the Spaniard.
Instead debilitating knee problems wiped out much of his year in 2009, which contributed to his only defeat at Roland Garros between 2005 and 2014 and meant he could not defend his hard-earned Wimbledon title.
In his absence Federer won his only French Open title and regained his crown at SW19 to take him to 15 slam titles, one clear of the record-holder Pete Sampras.
Federer wins: 4
Nadal wins: 7
Federer grand slams: 6
Nadal grand slams: 4
2010- 2014: The transitional years
After that horrendous run of injuries, Nadal re-established himself at the top of the sport in 2010 by winning three majors, though strangely none of them included matches against Federer.
It was a sign of things to come, as gradually slam meetings between the two foes became less and less common, and 2010 would prove to be the last time the pair would end a calendar year in the top two spots.
The arrival of Novak Djokovic, who won three out of the four majors in 2011, meant matches between Nadal and Federer were becoming rarer, and all the more cherished for that.
Unfortunately though Federer could not get a handle on his rival when the pair met in the most high-profile matches. Nadal won the French Open final in four sets in 2011, and was the victor at the Australian Open semi-finals of 2012 and 2014, in four sets for the former and straight sets for the latter.
The Spaniard was still hoovering up slams, and won eight in this period, but Federer picked up only two and none after Wimbledon in 2012. Djokovic and Andy Murray's improvement meanwhile meant Federer v Nadal matches were no longer solely finals. Twelve out of the 13 contests between the two has been finals between 2007 and 2010, whereas only two of the pair's 11 meetings were finals between 2011 and 2014.
Federer wins: 3
Nadal wins: 10
Federer grand slams: 2
Nadal grand slams: 8
2015-2016: The elder statesmen
By the start of 2015 Federer was 33 and Nadal 28, and both men were veterans of the tour whose best days were widely thought to be behind them.
Federer because of his age, Nadal because of his lingering injury problems and reduced explosivity. Neither won a grand slam in the period, and the pair met just the once - in the final of the ATP 500 event in Basel, with Federer winning in three sets.
Murray v Djokovic had emerged as the dominant rivalry in the sport, and it was regretfully accepted that Federer and Nadal had enjoyed wonderful careers but were unlikely to ever add to their grand slam totals.
Federer wins: 1
Nadal wins: 0
Federer grand slams:0
Nadal grand slams:
2017-?: Roger's revenge
Amazingly, despite both players coming into the 2017 Australian Open final on the back of injury-ravaged years, Federer and Nadal rediscovered their best form and both stormed to the final.
It was the dream contest for the tournament and most supporters, and the match did not disappoint. In an undulating match lasting more than three and a half hours, Federer eventually prevailed 6-4, 3-6, 6-1, 3-6, 6-3.
Since then Federer has completed three more wins over Nadal - in Indian Wells, Miami and Shanghai - and all without dropping a set.
Federer's four victories over his old foe last year means he has won five matches in a row against Nadal for the first time in his career.
A big reason for the turnaround has been Federer's much improved backhand, which has taken away Nadal's principal tactic of sending looping forehands into his opponent's ad corner and drawing errors.
As a pair, 'Fedal' were utterly dominant in 2017 - sharing the slams between them and claiming the top two spots in the rankings after Shanghai's final.
To think that just over a year ago the players were both injured and were on a tennis court together not for a competitive match but for the opening of Nadal's academy in Majorca.
Federer wins: 4
Nadal wins: 0
Federer grand slams: 2
Nadal grand slams: