Rafael Nadal greets Novak Djokovic at the net at the Rogers Cup in Montreal.
Rafael Nadal's win over Novak Djokovic at the Rogers Cup was his 21st victory over his Serbian nemesis.
Just a few years ago, Nadal was trying to break the riddle of Roger Federer on hard courts. Federer, once dominant over everyone, is struggling to stay relevant.
With any great rivalry, the tide can turn. Right now Nadal clearly has the edge over Djokovic. But does anyone have an edge over Nadal?
Let's examine who has the edge, right now, in the best rivalries in tennis.
Rafael Nadal and Roger Federer at the trophy ceremony in Rome.
Rafael Nadal has defeated Roger Federer twice already this year. He has a 20-10 head-to-head record against Federer.
The tide turned in this rivalry at the 2009 Australian Open. It was Nadal's first Grand Slam win over Federer on hard courts. Federer cried during the trophy ceremony, exclaiming, "God, it's killing me."
It was as if Federer knew his dominance was over and a new era had arrived.
Maria Sharapova looks at her runner-up trophy as Serena Williams beams after winning the 2013 French Open.
It's tough to call this a rivalry. Serena Williams has a 14-2 record against Sharapova. She's beaten Sharapova 12 straight times.
The only reason it's considered a rivalry at all is because they are the two biggest names in women's tennis. Williams would probably have to play well into her 40s for Sharapova to even this score.
Big edge goes to Williams.
Novak Djokovic congratulates Rafael Nadal after the match.
Rafael Nadal holds a 21-15 head-to-head record against Novak Djokovic. He has won five of their last six meetings.
However, he gained the upper hand on Djokovic at the Rogers Cup. It was Nadal's first hard-court win over Djokovic since 2010.
Edge to Rafa.
Victoria Azarenka congratulates Maria Sharapova at the 2013 French Open.
Because Serena Williams really has no rival, the next best thing is the battle for No. 2.
Victoria Azarenka and Maria Sharapova have traded places at No. 2 and No. 3 on the WTA rankings all season. Azarenka has a 7-6 record against Sharapova.
However, Sharapova defeated Azarenka in the semifinals of the French Open.
With both ladies recovering from injuries suffered at Wimbledon, I'd call this one a draw.
Andy Murray and Novak Djokovic during the 2013 Wimbledon trophy ceremony.
Djokovic will forever be linked to Andy Murray and his historic win at Wimbledon.
Djokovic holds an 11-8 edge over Murray. But Murray defeated Djokovic at the 2012 U.S. Open and Wimbledon. Djokovic beat Murray at the 2013 Australian Open.
These two account for three of the last four Grand Slam titles.
If not for Murray's decisive victory at Wimbledon, this one would be a draw.
However, coming off the Wimbledon win and heading into the U.S. Open as defending champion, Murray has the edge.
Serena Williams and Victoria Azarenka high-five at a WTA press conference in Cincinnati.
Serena Williams and Victoria Azarenka share a fun rivalry. Unlike the apparent venom between Azarenka and Sharapova, and Williams and Sharapova, there appears to be mutual admiration between these two.
On the court, however, their matches are competitive. Williams holds a 12-2 record against Azarenka.
Azarenka defeated Williams in Doha earlier this year.
However, Azarenka has not looked 100 percent since taking a fall at Wimbledon.
Edge goes to Williams.