Novak Djokovic hailed Rafael Nadal as his greatest-ever rival after coasting into round three of the French Open on Thursday.

The world number one had little trouble in overcoming Roberto Carballes Baena 6-3 6-1 6-2 in just over two hours on Court Philippe-Chatrier.

Speaking at a news conference after his victory, Djokovic was asked about his long-term foe Nadal, who has possibly played his final tournament at Roland-Garros.

Nadal, dubbed the 'King of Clay', was unseeded for the tournament due to a long injury lay-off and was beaten by Alexander Zverev in the first round.

But Nadal's legacy will be forever entrenched in Paris, having won the tournament 14 times, including beating Djokovic in three finals in one of tennis' best match-ups.

"He has been the greatest rival that I ever had," said Djokovic, who leads their head-to-head record 30-29.

"Matches against him on clay have frustrated me so much in my career, but they also made me a better player, made me understand what it takes to try to surpass him; try to win at least once or twice at Roland-Garros.

"It's the highest mountain to climb for me to win Roland-Garros, particularly because of Nadal, because I always have to win against him in order to get to the title. We had some really fantastic matches here."

Alongside Nadal and the great Roger Federer, Djokovic formed men's tennis' big three.

With Federer retired and Nadal in the swansong of his career, Djokovic - now 37 - concedes it is increasingly difficult to find the motivation to keep continuing at such a high level.

"It is becoming a little bit more challenging for me to push myself every single tournament to be really at the top," added Djokovic, who will face Lorenzo Musetti in round three in Paris.

"I did struggle with motivation on a constant basis to always have that motivation I've had for more than 20 years of professional tennis.

"I know the moment is going to arrive sooner or later when I'm just going to have off weeks, where I'm struggling to push myself or deliver what needs to be delivered. 

"My commitment to practice hasn't gone down. I'm focused pretty much solely on Grand Slams and Olympics this year, and playing for my country."