How could a human realistically fight someone much stronger and bigger

I'm writing a story, and my human charater butt's heads with a much larger and stronger monster.

While my charater does have experience fighting with other humans, he is obviously out matched in strength and size.

I would want the fight to be a fist fight, and my character doesn't really know how to fight, he can throw a punch or two, but has next to no experience?

How would I write the fight for my character to win without making him seem to strong for his circumstances.