South Africans Mark Murless and Tyrone Ferreira mastered the weather and the Royal Johannesburg and Kensington Golf Club's West Course to share the lead on day one of the Joburg Open.
In heavy rain Murless, who lives in Johannesburg, carded seven birdies and a solitary bogey on his way to a six under par round of 65.
The 31 year old was joined at the top of the leaderboard by compatriot Ferreira, who shot a flawless round which included three birdies either side of the turn.
Murless said: "My biggest challenge today was the weather, and just trying not to make mistakes.
"My plan was to pick up birdies on the par fives. So three under was my target, and I got three under that.
"I'm very happy with my start. If I can be two under tomorrow and for each of the next two rounds, I will be ecstatic."
Other players in contention include Wales' Sion Bebb, who is bidding to better the fourth place he achieved at last September's Omega European Masters in Switzerland - his highest ever placing in a European Tour event.
After a bogey-free round of 66, Bebb is tied for third place with Spaniard Pablo Larrazabal - whose brother Alejandro won the Amateur Championship in 2002 - and England's Ross McGowan.
Challenge Tour graduate McGowan, who claimed the Sunshine Tour's Rookie of the Year award last season, started his round with a bogey, but swiftly recovered with four birdies in the next eight holes.
He said: "It's not great out there - it's very tough, and it's difficult to judge your shots. You've got to carry the ball a lot further. The fairways are very wet, and there's not much run out there - maybe five or six yards. So I was trying to hit my drives higher."
One shot further back is a group of seven players including Paraguay's Marco Ruiz, who won the 102nd Abierto Visa de la Republica presentado por Peugeot in Argentina last December.
Ruiz is joined on four under par by England's Gary Lockerbie and Scotland's David Drysdale, as well as South Africans Garth Mulroy, Ryan Reid and Oliver Bekker.
Germany's Sven Struver, a previous winner of the Alfred Dunhill Championship at Leopard Creek, also carded a round of 67 after three birdies in his last four holes.
James Kingston, seeking back-to-back titles after his inaugural European Tour victory at the South African Airways Open last month, is also in contention.
The South African carded a three under par round of 68, which included an eagle three on the second hole.
Northern Ireland's Darren Clarke carded a two over par round of 73, whilst defending champion Ariel Canete was three shots better off after an opening round of 70, which featured four birdies and three bogeys.