By Rick Reeno

Former welterweight champion Carlos Quintana (29-4, 23KOs) has decided to call it a day. The Puerto Rican boxer announced his retirement on Saturday night, after suffering a fourth round TKO defeat to Keith Thurman (19-0, 18KOs) in an HBO televised fight at the Citizens Business Bank Arena in Ontario, California.

"This is the end for me, I'm not going to start again at zero," Quintana said after the loss.

The 36-year-old boxer was often brought in as the opponent, but every so often he pulled a rabbit out of his hat and scored an upset win - as he did in 2006 when he decisioned an undefeated Joel Julio and then in 2008 when he scored a major upset with a decision victory over an undefeated Paul Williams. He was thrown in with Deandre Latimore earlier this year on the Floyd Mayweather-Miguel Cotto pay-per-view undercard, and once again scored an upset with a fifth round TKO win.