“I played beautifully today and I’m delighted with it,” said McGrane, whose only European Tour title came by nine shots in China in 2008.“I got off to a fast start and I managed to keep it going and finish it off nicely.
England's Graeme Storm was also seven under with two to play, but the former British Amateur Champion saw a chip come back to his feet on the short eighth - his 17th - and after double-bogeying there he dropped another on the last.
Brothers Francesco and Edoardo Molinari, the only two players in the field currently qualified for The Masters Tournament in a fortnight, were on three under coming to the end of their opening rounds, while their fellow Italian Matteo Manassero and England's Robert Rock, both of whom still have a chance of making it to Augusta, were among the later starters.
McGrane's lead was trimmed to one when Otto, winner of the South African Open in November, birdied the 16th and 17th.
None of the three players involved in a play-off on the course last year managed to break par. Defending champion David Horsey had a 72, South African Jaco Van Zyl a 74 and Welshman Rhys Davies - winner in 2010 - a 75.
Edoardo won the battle of the Molinari brothers. He had a 68, Francesco a 70.
The 29 year old has made five cuts in five events on The European Tour, with a best finish of tenth in the Avantha Masters, as well as finishing fifth in the Mayakoba Classic on the US PGA Tour.
“I have been playing well so far this year and I am just waiting for everything to come together. I hope that this is the week it comes together,” he said.
“It was a good round today. It was very steady and I managed to putt well on the greens so all in all it was good. I didn’t play great last week but I managed to find a better rhythm on the greens this week and feel a lot more comfortable.”