Matt Kuchar and Harris English are in first place with a 14-under 58 after the first round of the Franklin Templeton Shootout.
Billy Horschel-Hunter Mahan and Graeme McDowell-Gary Woodland are tied for second with 59s at Tiburon Golf Club.
Kuchar and English opened with an eagle on No. 1 and followed with three straight birdies. They had two birdies from Nos. 5-9 and three straight birdies from Nos. 13-15 on the back nine. They finished with an eagle on No. 17 and birdie on No. 18.
Second-ranked Jason Day, who won last year's event with Cameron Tringale, withdrew last week.
Kuchar and English appeared to make a run at the tournament record of 55, set by Day and Tringale last year.