Boxing superstar Keith "One Time" Thurman says Manny Pacquiao needs to COME GET SOME ... claiming the fact PacMan is ranked above him is a big mistake.

The undefeated welterweight champ was out at Madeo when he responded to some trash talk from Manny's camp ... telling TMZ Sports plain and simple, "I'm ready to put hands on him!"

There's been talk of a potential matchup between the two -- Thurman clearly wants it.

Keith also says he's down for a rematch with Danny Garcia after their very successful prime time fight last month ... saying, "I did it one time. We can do it two times!"