Battling a bout of food poisoning, the Brit struggled on despite feeling drained and birdied his final two holes to sail clear of Australia's Matthew Giles.
"I woke up this morning, wasn't good at all. I had something bad to eat last night unfortunately, so I felt a bit weak out there today and it showed, I hit it terribly," he told reporters.
Fellow countryman Luke Donald had a difficult day too with a round of 70, making shots on some of the course's less forgiving holes but immediately surrendering them later in the round.
He remains confident going into the weekend, however:
"I hit a lot of good shots today but I've been struggling on the greens," he said.
"I'm finding it hard to see the line and missing my fair share of chances for birdie. Hopefully I'm saving them all for the weekend.
"I'm still in a decent position, I just need to get that putter going and get on a roll."
Meanwhile home favourite Geoff Ogilvy made the best round of the day with a 66 which leaves him at five under.
A slow start was quickly remedied with an eagle at the ninth for the Australian, and four more birdies on the back nine followed and he finished the day tied with Brendan Jones, Nathan Green, Brent McCullough, Kieran Pratt and Peter Lonard.