Derrick Lewis Training His Hot Balls Off to Go 5 Rounds with Cormier

Derrick Lewis says he's in the best shape of his life -- he's been training 3 hours a day to go the distance with Daniel Cormier ... and predicts a KO in the last few seconds of the 5th round!

Of course, Lewis famously said his cardio was terrible after his last second victory over Alexander Volkov earlier this month (he also complained his balls were hot) ... but he's been kicking his own ass in the gym and looks super leaned out.

"I'm training 3 hours a day instead of 30 minutes," Lewis tells TMZ Sports ... "I'm prepared to go 5 rounds."

Lewis and Cormier will square off for the UFC heavyweight title on Nov. 3 at UFC 230 -- and even thought Derrick's the heavy underdog, he's advising everyone to BET MONEY ON HIM!!

"I'm the underdog just about every fight," Lewis says ... "Whoever betting on me, I'm making you money!"

So, what's next for Derrick if he wins?