London - Novak Djokovic has been invincible so far this year but his assault on Rafa Nadal's world number one ranking could be about to hit the skids.
At least that is what common logic suggests as the clay-court swing begins and nine-times major winner Nadal gets the whiff of red European dirt in his nostrils.
Djokovic's surge to second in the rankings on the back of a 24-0 start to 2011, including the Australian Open title and victories over Nadal to claim the Indian Wells-Miami double, means Nadal is under pressure to repeat his 22-0 stampede through last year's clay-court grind.
Nadal still leads Djokovic by more than 3 000 points in the world rankings but the 24-year-old has 5 000 to defend over the next eight weeks or so, culminating in the French Open before the small matter of trying to retain his Wimbledon crown on grass.
Djokovic, with far less to lose after managing just one semifinal on clay last year, can head to Monte Carlo, his adopted home, swinging from the hip and ready to challenge Nadal for his clay-court throne.
"I've never beaten him on clay," Djokovic told reporters after his epic third-set tiebreak victory over Nadal in the Miami sunshine on Sunday.
"He's the king of that surface, the guy to beat. But I think I have the game to challenge him on that surface, and I showed that in 2009. I think we had some great matches in Monte Carlo-final, in Madrid-semifinal, so it is possible.
"If I do have an opportunity to play him on clay, obviously I have to be aggressive. Clay is the slowest surface that we have, and it's the surface that suits him best."
The way Djokovic was able to inject pace into rallies to stretch Nadal on Sunday was a telling factor and it is a tactic he will again try to use in the weeks ahead when he at least will not have to face the Spaniard until finals thanks to leaving Roger Federer behind in the rankings.
Djokovic and Nadal are head and shoulders above everyone else at the moment.
Federer is still a huge threat on any surface but defeats by those around him in the rankings are now becoming commonplace.
World number four Andy Murray is in a rut following his defeat by Djokovic in the Australian Open final while Swede Robin Soderling will do well to repeat his form on slow clay after bludgeoning his way to the last two French Open finals.
Worryingly for Nadal's rivals, the Spaniard looks to have overcome the physical problems that blunted his game until this time last year when he exploded into life.
His play against Djokovic, particularly in Sunday's third-set decider, would have been too much for any other player in the world apart from the irrepressible Serbian.
However, Nadal knows that not even his dominance on clay can go on forever and that, after a long stint on hard-courts, his natural instincts cannot be taken for granted.
"That's one time in (a) life to win every tournament on clay," Nadal said, referring to his feats of last year. "Nobody did that in history, only myself last year.
"It's difficult to imagine two years in a row to repeat that. The adaptation after almost 10 months without play on clay is hard the first days, so we will see.
"Hopefully I'm going to be playing well (in Monte Carlo). This is important for my confidence. I'm not going to win 10 times in a row Monte Carlo. That's for sure. I won six in a row and I'm going to try my best for the seventh."
Few expect Nadal to stumble on clay, but should the Spaniard show any chinks in his armour, Djokovic will be ready to pounce and eat into Nadal's rankings lead.
"The claycourt season is coming, so it's going to be interesting to see who's going to play some good tennis there," said Djokovic, who after Monte Carlo, Belgrade, Madrid, Rome and Roland Garros could be within touching distance of completing his mission to be the world number one.
ATP Top 20 rankings as at April 4:
1. Rafael Nadal (ESP) 12870 pts
2. Novak Djokovic (SRB) 9700
3. Roger Federer (SUI) 8550
4. Andy Murray (SCO) 5545 (+1)
5. Robin Soderling (SWE) 5420 (-1)
6. David Ferrer (ESP) 4600
7. Tomas Berdych (CZE) 3900
8. Fernando Verdasco (ESP) 2925 (+1)
9. Jurgen Melzer (AUT) 2660 (+1)
10. Gael Monfils (FRA) 2600 (+1)
11. Mardy Fish (USA) 2376 (+4)
12. Nicolas Almagro (ESP) 2350
13. Stanislas Wawrinka (SUI) 2320
14. Andy Roddick (USA) 2270 (-6)
15. Mikhail Youzhny (RUS) 2205 (-1)
16. Viktor Troicki (SRB) 1790 (+1)
17. Jo-Wilfried Tsonga (FRA) 1715 (-1)
18. Richard Gasquet (FRA) 1700
19. David Nalbandian (ARG) 1585
20. Sam Querrey (USA) 1520 (+1)