Roger Federer vs Rafael Nadal: The battle for No. 1 has only just started heating up

Roger Federer and Rafael Nadal are probably the two greatest players to have ever graced the game of tennis. They hold 20 and 16 Grand Slams respectively - the two highest tallies in the history of the sport - and have dominated the field in a way that no other player has.

That said, for a while it did seem that the Federer-Nadal duopoly in tennis was slowly but surely coming to an end, as Novak Djokovic rose to prominence. They said Federer was growing old and Nadal's injury troubles were too severe.

It seemed that the Fedal rivalry, which had captured the attention of the world for so long, was slowly fading into the sunset. But that was not to be.

The year 2017 saw these two legends fight against all odds and bring their 'A' game to the fore. 2017 will forever be known for the remarkable resurgence of two of tennis' finest exponents. With Federer clinching the Australian Open and Wimbledon and Nadal clinching the French and the US Open, the only question that was left unanswered was who would end the year as the number 1 tennis player.

There was some sort of anti-climax with Federer pulling out of the Paris Masters citing fatigue. This resulted in Nadal clinching the year-end World No. 1 ranking quite comfortably.

Come 2018, the battle for the top spot rapidly heated up with Nadal desperately trying to hold on to it and Federer trying to snatch it from him. At the Australian Open, the battle for the crown intensified greatly and a potential Federer-Nadal final seemed to be on the cards until an injury in the quarterfinal against Marin Cilic unfortunately derailed Nadal's campaign.

That paved the way for Federer to capture his 20th Grand Slam singles title. However, the win was not enough for him to clinch the No. 1 spot.

It was in the Rotterdam Open that Federer was finally able to become the oldest player to become World No. 1, as he thrashed Grigor Dimitrov in the final. Nadal on his part pulled out of the Acapulco Open due to injury, thereby enabling Federer to retain the top spot even longer.

However, Federer has faced a minor setback since then with back-to-back defeats - against Juan Martin del Potro in the final of the Indian Wells Masters and against qualifier Thanasi Kokkinakis in the first round of the Miami Open. This has resulted in him slipping back to the number 2 spot with Nadal ascending to the top.

With Federer having opted out of the claycourt season for the second successive year, Nadal will be the favorite to retain the No. 1 spot for a few months more - at least until the grasscourt season begins. But even a slight change in the script could shake things up considerably.

The difference between the two is less than 200 points, so if the Spaniard slips up even a little, Federer will be back at the top. If Nadal fails to win the French Open and at least two other Masters, he will surrender the crown to Federer yet again.

This timeless battle between these two legends is far from over, and it has certainly left tennis fans spell-bound. Who would have thought just two years ago that the top two positions in the ATP rankings would once again be the sole preserve of Fedal?