Much of the attention this week has been on Webb Simpson and his bid to beat world number one Luke Donald to the PGA Tour money title.
Simpson is just 67,980 US dollars behind Englishman Luke Donald, and needs to finish 15th or better in Georgia to lead the list going into the Children's Miracle Network Hospitals Classic at Disney World next week, where the pair will go head to head.
And while Simpson has not shirked the challenge, currently sitting tied for third, two shots off the lead after a one-under-par round of 69, it was Thompson who seized his chance.
He had three early birdies and then completed his round in cool-headed fashion, avoiding any bogeys to earn a 67 which put him a shot clear of second-round leader Horschel on 13-under 197.
"I'm very happy," Thompson told pgatour.com. "I played bogey-free on Saturday, which is always a good thing no matter where I stand."
Horschel was left kicking himself having found himself three shots in front at one stage only to eventually have to settle for a par 70, a double bogey on the par-four 16th being a key turning point.
He could count himself unlucky, to an extent, as he found a hazard on that hole.
"I guess the ball wanted to go in there," he lamented.
"It was a quick swing I get a little quick at the top. I'm fortunate to be as close to Michael as I am. I could be two or three shots behind. You can't win the tournament on Saturday. I'm one back and in the final twosome. It would be nice to be one ahead but I'll take it."
Trevor Immelman captured the crowd's imagination by equalling the course record with a 62 to put him alongside Simpson, at 11 under.
A group featuring Louis Oosthuizen (69), Jeff Overton (66), Kris Blanks (66), Nick O'Hern (69) sit at nine under.