Ken Duke and Cameron Tringale both shot first-round scores of 65 to secure a one-shot lead on seven-under at the Zurich Classic.
On a day of low scores in Avondale it was Duke and Tringale who stole the limelight, Duke shooting seven birdies in a bogey-free round while Tringale dropped a shot at the third before recovering to join his American compatriot at the top of the leaderboard.
Just one shot behind the duo on six-under are South Africa's Ernie Els, Sweden's Daniel Chopra and United States duo Steve Stricker and Chris Stroud.
Of the British challengers, Northern Ireland's Graeme McDowell and Scotland's Russell Knox are leading the charge after three-under-par rounds of 69 kept them within touching distance of the leaders.
Meanwhile, Masters champion Bubba Watson claimed "mental exhaustion" was hampering the defence of his Zurich Classic title after a one-under round of 71.
The 33-year-old has had a hectic month, winning at Augusta and becoming a father for the first time, both of which have taken their toll on the American as he shot four birdies and three bogeys to leave himself six shots off the pace.
Two shots back on Watson is Luke Donald after his bid to regain the world number one spot got off to a stuttering start, the Englishman carding a one-over-par round of 73.