Tommy Gainey and Johnson Wagner took advantage of good scoring conditions at Old White TPC in West Virginia to take the first round lead in the Greenbrier Classic.
The American pair carded eight-under-par first rounds of 62 to lead by two ahead of major winner Webb Simpson and Korea's Jin Park.
Rain before the event softened up conditions, allowing players to attack the pins, and Wagner enjoyed his front nine to the tune of 29 strokes, with five birdies including three in succession from the third.
He added another at the 11th which was followed by a pitch in for eagle, raising hopes of a round of 59, but six closing pars left him level with Gainey.
The latter changed his driver for the tournament and was accurate off the tee - vital with damp rough awaiting wayward drives - allowing him to card eight birdies including a run of two, three, three, three from the eighth.
Gainey told pgatour.com: "I missed one fairway today with this new driver and that says a lot because if I can hit fairways, I can score, I can really play this game. All of us can.
"All these guys out here, if we hit the fairways, we can score. Today with the soft greens, I made some putts."
A third American Simpson, the 2012 US Open champion, was bogey-free as he carded 64, a score matched by Jin.
England's Brian Davis and Greg Owen were the leading Britons after rounds of three-under.
This year's US Open joint runner-up Phil Mickelson, level par after 12 holes, suffered four dropped shots coming in, including a triple-bogey eight at the 17th.
Playing partners Bubba Watson (-2) and defending champion Ted Potter Jr, at one under, kept their round in check and are more handily placed to beat the cut.