The 22-year-old was only one off the all-time biggest margin of victory set by Tiger Woods at the 2000 US Open as he demolished the field at Barcelona's Real Club de Golf El Prat in amazing fashion on Sunday.
The 22-year-old Premlall made 10 birdies to shoot a second-straight round of nine-under 63 over the weekend and finish on 28-under par for the tournament.
Premlall's first win on the tour came in a season when he'd missed the cut in four of his eight appearances and not had a top-30 finish.
"I can't give myself enough credit today and I'm not really a person to say that — it was probably the most complete performance I've ever put through," he said.
By tapping in at the par-five last hole, Premlall added a 33rd birdie over his four rounds of 70-64-63-63.
"I have no words. I have worked so hard to get into this position and it's so rewarding to finally see the results of it," he added.
"The last eight or nine months have been such a struggle just to build myself onto a platform where I know I can give myself a chance to win and to end up in this position, I'm just so grateful and it's a dream come true."
Fellow South African Shaun Norris shot 68 and was second on 14-under.
Woods' remarkable US Open win at Pebble Beach in 2000 counts as a record for both the PGA and European Tours.
The only one to make the cut among the six-strong Australian contingent was Jason Scrivener, who finished on six under, tied for 37th, after his final-round 73.
