Tennis is rarely driven by rivalries alone. The tournaments and results speak for themselves. The champion of Wimbledon is still recognized as such, no matter who he beat to get there. Nobody values Roger Federer’s 2006 and 2007 Wimbledon titles more than his 2009 title, for example, just because he played Rafael Nadal in the final on the first two occasions.

But, when top players meet consistently, rivalries are formed that create a thrilling subtext for tournaments, fans, and even players. We don’t define tennis by the rivalries that it spawns, but the rivalries certainly have a draw of their own.

Because of the nature of the sport, most top players will have (at least) two or three main rivals whom they face often in later rounds of major tournaments. John McEnroe, Bjorn Borg, and Jimmy Connors were all rivals with one another.

Pete Sampras and Roger Federer are unique in that they each only had one main rival for most of their careers. Sampras dominated every major challenger except for Andre Agassi, while Federer did the same to all but Nadal. Federer’s records against Murray and Djokovic are not dominant overall, but Federer did dominate each of them in big tournaments during his prime. They might be his rivals now, but until 2009 or so the only player who could challenge Federer was clearly Nadal.

Now, though, we have an unprecedented tennis rivalry. Djokovic and Nadal have met 40 times, the most of any rivals in the Open Era. They first met in a Grand Slam final in 2010, near the end of Federer’s dominance of the non-clay areas of the sport. Since 2011, the pair have met 17 times, including 15 finals. Sixteen of those meetings were at Grand Slam or Masters 1000 tournaments. When these two meet, the stakes are always high.

It was in 2011 that Djokovic rocketed to the top of the sport. He was nearly unbeatable that season, and not even Nadal could slow him down. In their six matches that year, Djokovic won 14 sets to four. He played blistering tennis and, more importantly, was never afraid of Rafa’s forehand. He could beat Nadal from the baseline with his depth, defense, and power. No man, before or since, was able to beat Nadal in such a fashion as Djokovic did in 2011, particularly in the Madrid and Rome finals on red clay.

Since 2012, the rivalry has been more even. Djokovic is no longer the unbeatable force that he was in 2011, and even that tiny difference has been enough for Nadal to outplay him on many occasions. As this rivalry grows, though, the battle becomes more about the rivalry and less about the tennis. It becomes a mind game. Instead of each player bringing his best tennis, it can sometimes be a battle about finding each other’s weakness, even when that doesn’t suit each player’s style.

Their last few matches, though, have seen Djokovic return to near his 2011 form. He comfortably defeated Nadal in their last two matches of 2013, both on very fast indoor hard courts. But this week, in the slower hard courts in Miami, we saw a dazzling display from Djokovic for which Rafa really had no answers. Nadal couldn’t hit through Djokovic’s defense or work around him. He was beaten from the baseline, plain and simple.

The real test of where each of these two is now, though, will come at the upcoming Masters 1000 tournaments on clay. If Djokovic can dominate Nadal in those as he did at Miami, we may see this rivalry swing decisively in the Serb’s favor for the near future. Djokovic clearly has the momentum right now, but there is a huge difference between beating Nadal on hard courts and beating him on clay.

That is where the real test will lie.