The 31 year old Aussie had a great start with five birdies and an eagle on his first 11 holes to gain a buffer against the field in Doral, Florida.
A bogey in his 15th hole paved the way for Jason Dufner to join him on six-under when the young American birdied his final hole.
Scott likes this course and is gearing up for another serious run at the US Masters in a few weeks time.
“Obviously I’m very satisfied with the round today especially in these conditions,” Scott said. “I took advantage of my good play the first 11 or 12 holes and then managed to kind of get it up and down here and there coming in.
“I’m very pleased to put myself in the tournament so far. It’s a good way to start. “The last few years I’ve really got my head around this golf course and how to play it. I feel comfortable here. I look forward to coming here because it feels like you want to get playing good now. There’s a lot to play for here and in the upcoming weeks.”
Two behind the leaders were Dane Thomas Bjorn and South African Charl Schwartzel who both finished at four-under.
Rory McIlroy was playing his first tournament as world No.1 and promptly marked the event by recording his first over par round in five months.
“I know I shouldn’t have felt flat given the prestige of the event but it just felt that way out there,” McIlroy said after shooting a 1-over 73. “But at least it wasn’t disastrous. I just have to go out there tomorrow and post a red number.”
Tiger Woods tapped in for eagle on his opening hole but the found the going tougher as he progressed and finished with an even par 72.
Aaron Baddeley had a 3-under 69 to be tied for fifth as the second best placed Australian.
As he did on Sunday at the Honda Classic, Greg Chalmers had a great round going before stumbling late with a bogey, double bogey finish to end on 1-under tied for 21st.
Geoff Ogilvy – please someone tell him Movember is over – had a 73, as did Jason Day. There is no cut in this event but John Senden and Marcus Fraser finished four over and have work to do if they want to impress on the weekend.WGC Cadillac Championship Live Leaderboard