The 23-year-old Kilmarnock (Barassie) player started the closing circuit with a four-shot cushion and quickly increased his advantage on a course used for the Alfred Dunhill Championship on the European Tour by making three birdies in the first four holes.
But his hopes of a victory procession were scuppered when he then dropped five shots in three holes from the fifth, leaving him just two in front of the chasing pack as the leaders turned for home.
Admitting that he was feeling the tension, Walker steadied the ship as he started the back nine with a birdie before a chip in for an eagle-3 at the 13th then a birdie at the next gave him some breathing space again.
Some of that good work was undone by a bogey at the par-5 15th, but three pars to finish gave him a closing 71 and a three-shot victory from Swede Ludwig Alberg (68), with home player Garrick Higgo (71) a shot further back in third.
Walker is the second Scottish player to land this title in three years after Liam Johnston used his victory in 2017 as a springboard to getting on the European Tour this season.
“Today was an emotional roller-coaster,” admitted Walker, who finished with an 11-under-par 277 total. “I was really nervous during the round and the eagle on 13 put a bigger gap between me and the two guys I was playing with.
“At the time, it was absolutely huge and it allowed me to settle down, although it was still close. A lot of things went my way today and that chip in was one of them.”
He also produced a nice touch around the green at the last to save par after being fortunate not to see his third shot end up in the water as the ball stopped two inches from a potential disaster.
“I had a somewhat awkward yardage - 107 yards - and I took a club less,” he said. “I hit a smooth 54 degree and absolutely juiced it. I was quite nervous at that point and was just willing the ball to go on the green. I was really fortunate that it stayed out of the water.
“With my chip, I was thinking, ‘please don’t duff it and see it come back down the slope into the water’. I was going to be happy with anywhere on the green from there and I actually played a nice shot. The strike was perfect. I’ve been working on my short game a lot recently and I am glad in that moment it was very worthwhile.”
As well as Johnston’s victory at the same venue, Walker added to South African Amateur title triumphs by Michael Stewart, Brian Soutar, Daniel Young and Craig Ross in recent years as Scottish players have enjoyed lots of success in the Rainbow Nation.
“It feels absolutely amazing because it is something that I have been working towards my whole life, and particularly in the last two years where I have been full-time in elite amateur golf,” he added.
“It’s been a massive goal that I have not yet achieved in my amateur career and so to do have done that today is a fulfilment of a lot of hard work that I have put in. I am really delighted.”
Commenting on emulating Johnston by getting his hands on this trophy, he said: “I think that everybody out here would aspire to be a professional golfer like Liam on the European Tour and I think that a win like this certainly brings me closer to achieving that.
“I also think that playing this golf course shows me that I can compete on a Tour-like golf course and that’s very reassuring.”