Peyton Manning's single-season passing TD record is TOAST ... 'cause Patrick Mahomes is driving his Chiefs bus straight through it -- so says K.C. legend Tony Gonzalez.
Mahomes has lit up the league so far ... chucking 13 TDs in 3 games -- and Gonzalez tells TMZ Sports he thinks Pat will catch Manning's all-time mark of 55 in a single season.
"Right now, I'm looking at it, yeah," Tony tells us. "He's on his way!"
In fact ... the legendary tight end's been so impressed with Mahomes -- he's got him as MVP of the league for now ... with two other hot QBs right in the hunt.
By the way ... Tony also shared his thoughts on another Tony -- saying there's no way in hell Romo should make a comeback to the league.
"He's right where he should be," Gonzalez says.