Last year's runner-up, McKenzie stands one stroke clear of Chad Collins and Matt Bettencourt, who both shot 5-under-par 66 in their first rounds at Redwood Meadows Golf and Country Club.
Kevin Johnson, David Branshaw, Jason Schultz, Ricky Barnes and Chris Baryla are tied for fourth place one stroke further back at minus-four.
McKenzie finished second last year to Canadian David Hearn, who squeezed out a one-stroke victory for his first career title on the Nationwide Tour. McKenzie is also seeking his first win on tour at a course that has yielded one of his three career second-place finishes.
'I like the fact that it rewards someone who hits it straight,' McKenzie said of the 7,265-yard Redwood Meadows track. 'It doesn't reward the longer hitters any more than the shorter hitters.'
McKenzie, who ranks 36th in total driving on tour, took advantage of his fondness for the course, collecting eight birdies in his round to just two bogeys.
The 38-year-old began his day on the back nine and opened with a par before consecutive birdies at 11 and 12 moved him to 2-under. He two-putted for his birdie at the par-five 11th after reaching the green with a two iron, and then made birdie at the 12th with an 18-foot putt.
'It's setting up to my eye right now,' McKenzie said of his golf stroke. 'I had a lot of good chances, and I made a few.'
McKenzie collected his third birdie at No. 14 after knocking a sand wedge within three feet. He then dropped a stroke at the par-four 15th when he missed a 15-footer.
But a 20-foot birdie putt at the 18th put McKenzie at minus-three around the turn, and he moved further into red numbers by rolling in a 13-foot birdie try at the par-four first.
McKenzie stumbled to his second bogey with a three-putt at No. 3, but he managed to string together three straight birdies from the sixth to reach 6-under for the round.
'I guess I played pretty aggressive,' said McKenzie, whose best finish this year came two weeks ago at the Xerox Classic when he parlayed a third-round 64 into a tie for third place. 'I made a few putts and hit good shots. It was reasonably stress-free.'
Per-Ulrik Johansson, Joseph Alfieri, Keith Nolan, David Faught, Jason Enloe and Matt Gallant share ninth place at minus-three after each shot opening- round 68s. Eight golfers are tied for 15th place one stroke further back.