The South African, who lost out on the green jacket to Bubba Watson of the US on Sunday, was in a tie for third at the European and Asian Tour co-sanctioned event, two behind early leader Charl Schwartzel (64).
The duo looked refreshed ahead of their early tee time at the Kuala Lumpur Golf and Country Club.
They clearly enjoyed each other's company as they joked in the cooler morning temperatures.
"I feel like I'm swinging it well and I'm used to a lot of travel so you adapt quickly," Oosthuizen, who is the 2010 British Open champion, said after his round.
"We knew there would be one tough round and it is normally the first one. It was lucky it was earlier so we could have a nice rest in the afternoon."
Playing partner Schwartzel, who finished 11th here last year after he had gone one better than his compatriot and won the Masters title, produced nine birdies in his round as he took the lead at the $2.5-million event.
"Verygood," was Schwartzel's review as he looked to win his first title since his Augusta triumph.
"I have worked hard for the last couple of months and haven't had anything happen for me," Schwartzel said.
"But it has been feeling good for a long time and today I seemed to put it together. Eight under is a good score for me."