Jason Day’s caddy has been forced to withdraw midway through his round at the PGA Tour Championship due to injury.

Jason Day not only survived but thrived in his first professional round of golf without Colin Swatton on his bag.

The 26-year-old Day played the last 11 holes of the opening round of the Tour Championship without his regular caddy after Swatton succumbed to a sacroiliac joint injury, forcing mental coach Jason Goldsmith to take over on the bag.

Despite the hurdle he still fashioned a three-under 67, bogey free over the last 12 holes, to be tied third just one shot off the lead.

While most tour players could cope with the change, the Swatton-Day relationship is unlike any other in the game, given he is also his swing coach and father figure, having taken the Queenslander under his wing as a teen.

Swatton was a golf instructor at Day’s boarding school, where a troubled Jason had been sent after the death of his father, starting a relationship that has blossomed to the PGA Tour.

He was also Day’s best man at his wedding and has caddied in every one of Day’s 601 professional career rounds, not to mention countless efforts in Day’s amateur career.

So Day would have been forgiven for being nervous when Goldsmith jumped in from outside the ropes.

“JG (Goldsmith) didn’t know what to do really but he did a really good job,” Day said.

“It was kind of something where it just kind of clicked and it worked.

“I did all the yardages out there and we were just talking, kind of just going about things our way, and that kind of calmed me down a little bit.”

Goldsmith has been working with Day for almost two years as his mental coach, famously using brain wave readings to help his charge focus more intently.

He also helps Swatton before tournaments with green reading and mapping, making him the logical short notice fill-in.

“Col had done all the work so all the numbers were already there so it was a real easy job. Col made sure I knew what all the adjusted numbers were and how they were written in the book so it was fun and it went by too fast to be nervous,” the 46-year-old Goldsmith said.

“I think being his mental coach he felt comfortable rather than someone else doing it. It wasn’t like I was coaching him along the way, he knows what he’s doing.”

Despite Day being three-under without Swatton he was looking forward to having his regular man back for Friday’s second round, saying he expected him to be his caddy “until he wants to fire me.”