Rafael Nadal played what may potentially be the final singles match of his career late on Friday, perhaps fittingly, against the player with whom he formed the most formidable rivalry of the decade gone by, and perhaps the greatest in men’s tennis. Nadal went down 2-6, 6-7 (5) to Novak Djokovic at the Six Kings exhibition tournament in Riyadh. The Spaniard had earlier announced that he will retire from professional tennis after playing for Spain at the Davis Cup finals next month. Following their final clash, the duo shared a warm embrace at the net and some graceful pleasantries in stark opposition to the fiery battles they have had on tennis courts for nearly 20 years. “Thank you Novak for everything, for all the moments we shared on court during our careers. It’s been an amazing rivalry,” Nadal said, per Reuters. “In a personal way, you helped me go over my limits during almost 15 years. Without that, I wouldn’t be the player I am today. Congratulations for all the titles and amazing career to …