The opening round was delayed shortly after it began by a thunderstorm that contained destructive downbursts of wind.
Two television towers and the $150,000 cameras on them were destroyed. One of the cameras wound up submerged in a nearby lake. At least 17 palm trees were felled by the winds and the 18th hole scoreboard was turned into a pile of rubble, but no one was injured.
Charley Hoffman was one of just 11 players to finish his round and he turned in a 5-under 67 to share second place.
Also at 5-under were Vijay Singh through 16 holes, Nick Watney through 16, Ryo Ishikawa through 12, Matt Kuchar through 11, Martin Kaymer through 10 and Luke Donald through 10.
Kaymer, ranked No. 1 in the world, and Donald, the third-ranked player, were in the same pairing along with second-ranked Lee Westwood, who was 4-under.
The threesome of Phil Mickelson, Tiger Woods and U.S. Open champion Graeme McDowell were through 15 holes and none was threatening the lead. Mickelson was 2-under and both Woods and McDowell were 1-under.
After the storm blew through, the winds dropped and scoring conditions proved ideal.
"I guess with that storm it brought some tranquility to the golf course, because there was just no wind," Mahan said. "With good players and a good golf course and benign conditions, you're going to have some good scores."