VIDEO: Isaiah Thomas tops Floyd Mayweather in best-of-5 basketball series

With Floyd Mayweather's 49th and final career fight just two weeks away, Showtime Sports' "All Access" caught the welterweight champion finally losing at something.

In a teaser for the first episode of the series, which will air Friday, Mayweather drops a best-of-five basketball series to Boston Celtics point guard and friend Isaiah Thomas. After Mayweather claims to have taught Thomas everything he knows, a heated game between their teams ends with Thomas dishing the game-winning assist and yelling "48-3!"

It's not the first time Thomas has made a clutch play and taunted his pugilistic pal, who has been very supportive of Thomas online.

While the 26-year-old Thomas is entering his prime ahead of his fifth NBA season, the 38-year-old Mayweather will look to close out his career a perfect 49-0 when he stands opposite Andre Berto on Sept. 12.