Former champion Bubba Watson took the halfway lead at the Travelers Championship after overcoming an unsteady start, but Padraig Harrington was hot on the American's heels in Connecticut.
Watson, who recorded his first career victory at the TPC River Highlands in 2010 and was runner-up last year, started on the back nine in his early-morning start and opened with a bogey before warming to his task thereafter.
The 2012 Masters Champion picked up birdies at the 13th, 16th, third and sixth holes to move to 10 under overall after his 67.
"I was a little sluggish, waking up dead early after playing a good round, not really sleeping very much," said Watson on the PGA Tour website
"I was stiff at first, it showed the first few holes. I knew it was going to be a tough day, I made some putts and I just tried to play as steady as I could play.
"I love this place, I've always played well. It suits my eye. The tee shots, there's nothing that's too scary for me, it's treated me nicely."
Three-time major winner Harrington was two shots back alongside Watson's fellow American Patrick Reed, both of whom shot 66s for the second day in a row.
"I was a little sluggish, waking up dead early after playing a good round, not really sleeping very much" - Bubba Watson
After approaching the back nine on one under, Harrington's fortunes took a turn for the better with a run of four birdies in five holes, starting from the 12th, that moved him just one shot off the lead.
However, a bogey at the par-four 17th dropped the Irishman back to eight under overall.
Reed endured similar fortunes by carding five birdies in 17 holes before blotting his copybook by dropping a shot at the last.
It was a day to forget for overnight leader Hunter Mahan, however.
The 31-year-old looked to be in a rich vein of form after following up a joint-fourth finish at last week's US Open with a stunning opening round of 62 yesterday, but he could only manage a disappointing 71 today.
That dropped the American back to seven under alongside compatriots Tommy Gainey and Tag Ridings and Australian Nick O'Hern.
US trio Charley Hoffman, Keegan Bradley and Webb Simpson and Zimbabwean Brendon de Jonge were one shot further back, while the man who succeeded Simpson as US Open champion last week, Justin Rose, was one of 12 players on five under.
Fellow Englishman Lee Westwood made the cut with nothing to spare after a disappointing round of 73 dropped him back to level par, alongside compatriot Gary Christian.