Grigor Dimitrov shot up the rankings in 2017 from No. 17 to No. 3. Obviously, the Bulgarian has improved many elements of his game, but one key statistic stands out. 

A lot is made of the second serve, and how important it is to have a reliable one, but what about the second serve return? 

In 2016, Dimitrov won 48.2 percent of his second serve return points. In 2017, he bumped that stat up to 52 percent, joining the Top 10 of second serve returns on tour. The list is led by Diego Schwartzman and Rafael Nadal (who both have over 55 percent). 

According to the ATP, the best results come when the shot is aimed toward the middle of the court and the main lesson is clear "improve your second serve return and a better ranking comes with it."