Seeking his third victory in the elite event hosted by Tiger Woods, McDowell launched his title defence with a level-par 72 to end the opening round in a tie for sixth, five strokes behind pace-setting American Zach Johnson.
"Generally I was quite happy the way I hit the ball," McDowell said after offsetting four birdies with four bogeys on a sun-drenched but chilly day at Sherwood Country Club in the foothills of the Santa Monica Mountains.
"I hit a few squiffy ones, but there's room for improvement. Get back out there tomorrow and there are lots of birdie opportunities on this course.
"I think that's why I've always enjoyed it, why I've always felt comfortable on it. It offers you a lot of chances if you play decent."
The Northern Irishman clinched the World Challenge for the first time with a playoff victory over Woods in 2010, six months after landing his maiden major title in the US Open held at Pebble Beach.
Last year, McDowell once again triumphed at Sherwood, holding off American playing partner Keegan Bradley to win by three shots.
"My last eight rounds around here have been in the 60s," smiled the ever-popular McDowell. "But this is a tough golf course this week. The course hasn't been this tough in a couple years. The scoring reflects that.
"The greens are much firmer and the speed of them caught me by surprise a little bit today. My (putting) speed was a little clumsy, and it showed today on the greens."
The World Challenge will be shifting to Orlando in Florida next year, ending a run of 14 successive editions held at Sherwood, and California fan McDowell expressed bitter-sweet emotions about the move.
"Obviously I like Sherwood a lot," the 34-year-old Northern Irishman said. "Every time I've been here I've been very fortunate to play well. Orlando is my backyard these days, my hometown, and I guess I have mixed emotions.
"But I think this is a great event and any change sometimes can be a good thing - from an energy point of view, for the event's popularity.
"The people here in California have enjoyed this event but I think the people in Orlando will certainly enjoy it next year."