Defending champion Fredrik Jacobsen led the way after play was suspended due to inclement weather at the Travelers Championship in Cromwell, Connecticut.
Rain and thunderstorms battered TPC River Highlands for much of the day, causing a stoppage of over an hour early in the day and forcing the players off the course for good at 3.19pm local time. Play was officially called off at 6.30pm (2330BST).
Jacobsen was among the 76 players to complete their second rounds, with 77 more needing to resume tomorrow.
And in a direct echo of last year's event, he led at the halfway stage on nine under par after following up his opening 65 with a 66 today.
Starting at the tenth, an opening par preceded two birdies and an eagle, though he immediately gave one shot back at the 14th.
Two more birdies followed on the front nine before a closing bogey left him just one shot ahead.
"It feels good to have some birdie chances," he told pgatour.com.
"You play the US Open, I like that kind of golf but you play for four days and you grind it out. It's nice to have a couple of holes where you feel like if you hit the shot you have some good chances to make birdies."
Tied for second on eight under are Australian Nathan Green, three under for his front nine today despite starting with two bogeys, and Charley Hoffman, who carded five successive birdies from the 11th to be five under through six holes when the weather cut him off in his prime.
US Open winner Webb Simpson was in the clubhouse on five under following a 69 today, with his playing partners and fellow major winners Keegan Bradley (68) and Bubba Watson (71) four under and three under respectively.
The second round will resume at 7am (1200BST) tomorrow and the third round will begin immediately after the cut, which is projected at level par at this early stage.