Paul Peterson opened a two-shot lead before the opening round was suspended due to a waterlogged course at the Joburg Open.
Peterson fired a blemish-free 62 on the West Course to move two clear of English pair Aaron Rai and Paul Waring, who were playing the East Course.
Romain Langasque was one of three players a further shot back on six under, with defending champion Haydn Porteous five strokes off the lead with five holes to play.
Heavy rain had soaked the course through much of the week and returned midway through the morning session, leading to play being halted at 2.35pm local time (12.35pm GMT) with 98 players still on the course.
Peterson made the most of the early-morning drier conditions with four birdies in his opening six holes, with the Czech Masters champion adding another at the ninth to reach the turn in 31.
The American holed an eight-footer at the 14th and birdied the par-five next, before nudging in from nine feet at the 16th and adding a ninth gain of the day at the last.
“It was fun out there today,” Peterson said. “I’ve been putting a lot of really good work in with my coaches and the consistency is getting better.
“I’ve always been someone who putted pretty well and hit good drives, but my iron play is improving, my wedge game is improving and when I’m missing greens I feel really really confident with what I’m doing around the greens.”
Rai signed for a bogey-free card in just his third European Tour start, with Waring birdieing three of his final four holes to join the share of second.
This week’s event is the third tournament of the 2017 Open qualifying series, where three players inside the top 10 in Johannesburg – who are not already exempt – booking their place in the third major of the year.
Jbe Kruger, one of only three players in the field already qualified for Royal Birkdale, closed a blemish-free 66 to join Langasque and Sebastian Soderberg in tied-fourth.
Former Ryder Cup captain Darren Clarke was two-over after 14 holes, with the Northern Irishman one of 98 players set to finish their round on at 6.45am local time (4.45am GMT) on Friday morning.
The deadline is fast approaching for fans to take advantage of early season pricing on tickets for The 146th Open at Royal Birkdale. Simply buy before midnight on the 28th February at TheOpen.com/tickets.