Baker's story is pretty incredible -- he went from being a walk-on at Oklahoma to being the reigning Heisman Trophy winner. He threw for 129 TDs and just 29 interceptions in his college career.

Now, Mayfield has been given the task of turning around a miserable Browns franchise, which has combined for 4 total wins in the past 3 seasons ... including ZERO in 2017.

The next top picks in the draft are expected to be Saquon Barkley, Bradley Chubb, Quenton Nelson and of course ... fellow QBs Sam Darnold, Josh Allen and Josh Rosen.

BTW -- commish Roger Goodell got booed heavily once again when he walked out to open the Draft, even though he was joined by a group of Dallas Cowboys legends ... in Texas! Roger Staubach, Troy Aikman and Jason Witten got their cheers later, though.

Baker was clearly overjoyed by the selection ... breaking down in tears when he found out he was going to Cleveland.