He only dropped three shots over the four days and improves on his previous best European Tour finish of third at the 2015 BMW International Open.
Saddier, a 25-year-old whose only professional success came in the second-tier European Challenge circuit two years ago, scored an eagle and seven birdies to roar into contention.
Saddier joined Paisley at the top of the leaderboard after the Englishman earlier followed up a first-round 66 with a near flawless 65 in cloudy conditions.
"I got frustrated out there to be quite honest", he said of his front nine.
"I'm just so happy with how the week went and to get the win", Paisley said.
Englishman Paisley was full of praise for his rookie caddie after holding his nerve with a superb blemish-free six-under final round of 66 to be crowned champion by three shots on Sunday. "That puts me under pressure when I'm practising and I think it was one of the big keys to how I handled the pressure today", the slender Paisley said.
3 - Home player Hennie Otto looked like having a great chance of setting a course record in the final round, having posted 10 birdies through his first 16 holes.
"I eagled the second and kind of kept it going from there". "After a seven-week break, when I came out to practice on Tuesday morning and in the pro-am in the afternoon, I didn't really hit it great", he said.
In a field containing five former Major winners, Saddier and Paisley will be thrilled to lead the pack in the second oldest national golf championship after the British Open.
A far more settled back nine produced a birdie and another eagle, a record third for Grace during a European Tour round.
Trailing by five strokes at the halfway stage, Grace needed a low third round to keep alive hopes of back-to-back European Tour triumphs in his homeland.
Ernie Els, a five-time victor of the South African Open, made the cut after a 70 moved him to 3 under.
Retief Goosen, a two-time US Open victor, faltered at the last on Friday with a double-bogey six and lost further ground on the field with a one-over 73 to finish at seven under heading into the final round, while Ernie Els carded a two-under 70 to sit 10 shots off the lead at five under.
But ex-US Masters champions Mike Weir (146) of Canada and Trevor Immelman (149) of South Africa bowed out after the second round.