James Harden & Craig Sager -- Emotional Reunion ... At Rockets Media Day

Cool moment in Houston today ... when James Harden went out of his way to track down NBA broadcaster Craig Sager so he could give him a hug as Craig continues to battle cancer.

It all went down in Houston ... where Sager has been receiving treatment for leukemia ever since the cancer returned back in March.

Sager hopes to return to the NBA sidelines this season -- and judging by his outfit, he's already getting wardrobe on point ... rocking a weird ugly shirt -- 'cause that's how Sager rolls.