Forty years old and already in the twilight of his career, yet Manny Pacquiao has decided to take on a challenging fighter in Keith Thurman.

He knows the brash American owns a mean overhand right and is 10 years younger than him, but Pacquiao’s instincts tell him he’ll be able to find ways to crack Thurman.

"I like the fight because it's a challenge for me, but I know I'm going to win," Pacquiao said in an article posted on BoxingScene.com.

He said the secret to his longevity has always been his work ethic.

• READ: Hall-of-fame referee of key Pacquiao fights picks ‘Pacman’ to KO Thurman

"I just focus on discipline and work hard," said Pacquiao. "Don't think about anything else but the training. Boxing is all about focusing and working hard. Nothing else.”

They said when training is hard the fight would be easy and Pacquiao agrees.

“If you're thinking about anything except preparation and training and your workout, you'll forget about boxing. Boxing is about how you punish yourself," he said.

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