3. Keith Thurman (26-0, 1 no contest, 22 KO’s)
The reigning WBA Welterweight Champion has been on a tear over these last few years. He dominates his opponents from start to finish, his longest fight since 2009 has been 10 rounds, and his opponents have had great difficulty trying to land a punch on him. Thurman can easily be Mayweather’s biggest physical challenge.