It is Scott's first tournament back in Australia since his win at Augusta.
He'll play the next three weeks in home tournaments: the Australian Masters and the World Cup of Golf, both at Royal Melbourne, and the Australian Open at Royal Sydney.
"I put a real focus on getting ready the best I could for this event and wanting to play well," Scott said. "I am in pretty good shape at the moment."
Scott, starting on the back nine, eagled the par-5 12th to move into a share of the lead with McKenzie.
A birdie at the par-4 fourth put him into the lead for good during the round.
Scott was honoured yesterday with "Green Day" as spectators and many players wore something green to commemorate Scott's playoff victory at the US Masters in April; the first Australian to win a green jacket.
"The PGA wanted to make today a green day and everyone embraced it, even the players. Which is really special for me that my peers would do that," Scott said
- AP