His San Francisco Giants may be struggling to defend their World Series title, but the reigning National League MVP is enjoying a personal milestone in 2013.

Posey has the best-selling jersey in Major League Baseball, ahead of future Hall of Famer Mariano Rivera.

Posey is the head of a class of youth – of the top 20 jerseys, only two belong to players over 30, Rivera and his Yankees teammate Derek Jeter (number 7).

Interestingly, the New York Mets, while struggling to reach .500, have a pair of stars in the top five – David Wright and rookie pitching sensation Matt Harvey.

Speaking of rookie sensations, Los Angeles Dodgers outfielder Yasiel Puig checked in at number 10 on the list, despite not even being on the roster when the season began.

The 10 best-selling Major League Baseball jerseys

1. Buster Posey – Giants
2. Mariano Rivera – Yankees
3. Yadier Molina – Cardinals
4. David Wright – Mets
5. Matt Harvey – Mets
6. Bryce Harper – Nationals
7. Derek Jeter – Yankees
8. Manny Machado – Orioles
9. Mike Trout – Angels
10. Yasiel Puig - Dodgers