Rookie Brett Stegmaier stormed to the top of the Shriners Hospitals for Children Open leaderboard as Englishman Greg Owen saw his challenge fade in the second round.
Stegmaier, playing in only his fourth PGA Tour event, was six under through 15 holes but was unable to finish his round as the light faded in Las Vegas.
An eagle on the 16th - his seventh hole of the day - accompanied four birdies before play was abandoned for the day at 6.05pm local time.
The 32-year-old will come back at 8am on Saturday morning looking to stretch further his one-shot advantage from fellow Americans Tyler Aldridge, Chad Campbell and Morgan Hoffman.
But it was bad news for Owen who started the day a shot off the lead but ended it eight adrift after a three-over 74 left him on three under, alongside Scottish pair Martin Laird and Russell Knox.
Rickie Fowler tied for the best completed second round, with his six-under 65 including an outrageous 79-foot putt for eagle on the 13th.
The 26-year-old American is in 27th position, six shots off the lead, as he fights back from his one-over first round.
Michael Thompson, one of four joint leaders from the opening round, fired a 73 to slip six shots back, while Argentinian Emiliano Grillo - who was aiming to become the first player to win the opening two events of the PGA Tour season since 2003 - looks set to miss the cut after a second-round 71 left him two over par
