The tournament is part of the European Tour schedule.
Hugo, who endured a rough 2002 campaign, carded six birdies without a bogey. The 1998 South African amateur champion birdied three of his final six holes to seize the lead. After finishing 34th on the Order of Merit in 2001, Hugo fell to 120th last year.
"I'm glad I played well today to prove to myself, rather than anyone else, that I can still do it," Hugo said.
Clark is the defending champion and Kingston finished tied for second here a year ago. Former British Open champion Peter Lawrie of Ireland, England's Iain Pyman, Holland's Rolf Muntz and Scotland's Andrew Coltart and David Drysdale were two strokes back.
Clark also enjoyed a bogey-free round.
"I don't think being defending champion has adversely affected my golf," Clark said. "Quite the reverse in fact. I felt comfortable all day."
Pyman was 6-under with three holes to go but double-bogeyed No. 16.
"It was a disappointing way to finish but overall I'm pleased to shoot 4-under," Pyman said.
Lee Westwood carded a 3-over 75.