Michael Kim was four shots clear at the top of the leaderboard with a hole to play when weather halted the second round of the John Deere Classic.
Pursuing the first win of his PGA career on 16 under after 35 holes, the American, 25, was on course to seal a considerable advantage after taking the top spot from countryman Steve Wheatcroft.
Keeping a clean card on Friday, Kim notched up eight birdies over the 17 holes and will finish off his second round on the par-four 18th on Saturday morning.
Round two in Illinois proved to be a more challenging affair for day one leader Wheatcroft, who slipped into second with a three-under round of 68.
He was tied on 12 under with Canada's David Hearn, who carded 64, and Johnson Wagner of the US who went round in 66.
Italy's Francesco Molinari, who won the Quicken Loans National a fortnight ago, shot a 66 to sit tied for fifth with America Bronson Burgoon and Matt Jones of Australia on 10 under overall.
An eagle on the second helped Jones on his way to an eight-under round of 63 - the joint-lowest of the day with John Huh of the US, who finished in 12th on nine under overall.
Ireland's Seamus Power replicated his 68 in the first round to sit tied 24th on six under, while Englishman Brian Davis was projected to just miss the cut after a round of 71 left him tied for 82nd on two under.