By Tzvi Machlin Few rivalries in tennis history can match the one between Novak Djokovic and Rafael Nadal as they both try to reach the pinnacle of the sport. But that didn’t stop Djokovic from giving Nadal his props today. Taking to Twitter, Djokovic congratulated Nadal on winning the Australian Open for his 21st Grand Slam this weekend. He praised Nadal for his “fighting spirit” and also complimented his Finals opponent Daniil Medvedev for giving him a tough match. “Congratulations to [Rafael Nadal] for 21st GS. Amazing achievement. Always impressive fighting spirit that prevailed another ti…