Larry Holmes Says Mike Tyson Wasn't Toughest Opponent, It Was Ken Norton

Mike Tyson is the only man to ever knock out Larry Holmes ... still, the boxing legend tells TMZ Sports "Iron Mike" ain't the toughest fighter he fought.

Holmes was a beast in the ring who scrapped with Tyson, Holyfield, Spinks and just about every other dominant heavyweight of his era. So, when we saw him in NYC, we asked if Mike was the hardest guy he ever faced.

His answer ... nope.

"My toughest opponent was Kenny Norton. I fought Mike Tyson, I was kinda over the hill a little bit. I had retired then I came back and fight Mike Tyson. I really wasn't in that good of shape."

"If I could do it all over again, I'd take more time and do it right."

FYI, Holmes -- 69-6 as a professional -- was 39 years old when he was dropped 3 times and KO'd by Tyson in the 4th round of their January 1988 fight.

In his 75 pro fights ... it's the only time Holmes was knocked out.

As for his 1978 fight with Norton ... it was a 15 round war that Holmes won by split decision -- earning him the WBC heavyweight title.

We also hit Holmes with a question about the ultimate dream fight -- Muhammad Ali vs. Mike Tyson -- in their primes ... and asked who'd win.

"Mike Tyson would get beat up 'cause he's a face fighter. He comes in down low, and Muhammad Ali is a jabber," Holmes says ... "He'd get that jab in there just like he did with Joe Frazier. So, Mike Tyson would have to get around that jab, and he'd have a lot of problems getting around that jab."