In another testimony of his incredible legacy, the 21-time Major champion Rafael Nadal is spending his 18th season in the top-20. In December, the Spaniard entered an exclusive group with 850 weeks in the top-20, and he made another milestone this week.Rafa is counting his 861st week in the top-20, becoming the fourth player to achieve that after Jimmy Connors, Andre Agassi and Roger Federer, who leads the field with 1064. An 18-year-old Nadal was ranked just outside the top-50 at the beginning of 2005, hampered by injuries in the previous season and determined to show his full potential.After reaching the Australian Open fourth round, a teenager conquered Costa do Sauipe and Acapulco on his beloved clay in February to gain a boost. Rafa skipped Indian Well …