French Open Preview: 3 things you need to know about the men's tournament

The second major of the tennis season is upon us, as the French Open begins Sunday in Paris.

Men's tennis in 2015 can be summed up in two words and one name: Novak Djokovic. The French Open over the past decade, meanwhile, has been defined by two other words and a different name: Rafael Nadal.

Related: 3 things you need to know about the women's tournament

The question on everyone's mind heading into Roland Garros: Is the King of Clay's reign over? We're going to find out, one way or the other, over the next two weeks.

Here's what you need to know about the men's tournament:

A once-impenatrable grip loosens

It's almost jarring to see, the "[6]" next to Nadal's name on the official French Open draw. It's the lowest the Spaniard's ever been seeded in Paris, because he owns Roland Garros.

It's almost worth saying out loud, to give the numbers, the accomplishments, more weight: Nadal's won five straight French Open titles, and nine of the last 10. A decade of dominance.

Ten years is a long time. It's worth remembering. Nobody stays on top forever, and nothing but time is undefeated. Nadal, only 28, also worth remembering, somehow ranked seventh in the world, has begun his decline.

But there's something different about Nadal in Paris. The doubts were there last year, too, although they're certainly stronger this year, but Nadal remains the champion. The King. Grantland's Brian Phillips wrote it best:

The idea that (Nadal) could win here seems impossible. The idea that (Nadal) could lose here seems impossible.

The romantic tennis fan wants to see Nadal win again. Everything ends, so what's another year on top? But the facts are harder to ignore this time around: Nadal's 25-9 in 2015 - he lost 11 matches last year, his worst on tour, and lost 13 combined in 2012 and 2013. His one title this year was won on clay, in Buenos Aries, but five of those nine losses have come on the surface he's come to dominate. And he's in Djokovic's draw. And Andy Murray's half.

What Phillips said, in other words: The impossible will happen at Roland Garros.

Djokovic's best shot

Based on the last two years, it's hard to believe Nadal, who will turn 29 on June 3, is only a year older than Djokovic. Two of the men who make up the Big Four, they are trending in opposition directions, which makes 2015 undoubtedly Djokovic's best chance at completing his career Slam.

Fatherhood agrees with the Serb. He's playing the best tennis of his life. He heads into Paris with a 35-2 record and five titles, including the Australian Open, and Masters 1000 wins on clay in Monte Carlo in April and Rome in May.

The surface doesn't matter: Djokovic is the best men's tennis player in the world, in a league of his own, creating separation atop the world rankings. The Big Four may no longer exist. There's Djokovic and everybody else.

But in order for Djokovic to win at Roland Garros, he'll have to go through Nadal, a quarterfinals match looming. Nadal's a stupendous 66-1 at the French Open. It can't ring any more true: to be the best, you've got to beat the best. We're sure Novak wouldn't want it any other way, to win the French and give Nadal loss number two.

The others

The men's game is seemingly always about a character or two, with so many left behind. How do you write about a Grand Slam and not mention Roger Federer? Well, you don't. Federer isn't expected to win at Roland Garros, but he's got a favourable draw, and is 25-9 on the season, including 9-3 on clay. Has a No. 2 seed at a Grand Slam ever been considered such an afterthought? Don't sleep on Fed. He deserves better.

Murray's a clay-court champion for the first time in his career, and joined only three other men to ever defeat Nadal on the surface in a final in Madrid. He's 10-0 on clay in 2015. The Prince of Clay?

While Milos Raonic had to withdraw from the tournament, Tomas Berdych arrived in Paris ranked fourth in the world and with a 32-9 record in 2015. But in order for him to get over the hump, he'll have to make hay against the best: Berdych is 2-9 against top-10 opponents this season.

Kei Nishikori is 31-7 this season, and 10-2 on clay, but his 3-5 record against top-10 opponents means he isn't quite there yet, either. David Ferrer's in the same boat: 32-7, but 2-5 against top-10 competition.

And that's why the men's game remains the same. One group's always trying; another, more select group's always winning.