Shane Lowry is five shots behind leaders Byeong Hun An and Brendan Steele at the Waste Management Phoenix Open.
The Irishman birdied the third, 10th, 13th and 17th hole to end up on five under, which included a bogey on the fifth hole, in the second round.
However, Padraig Harrington has missed the cut in the States after bogeying the final hole to finish at one over par.
Korean An and American Steele both birdied three of the last four holes on TPC Scottsdale's Stadium Course to reach 10 under par in Arizona.
An, who shot to prominence when he won the European Tour's BMW PGA Championship at Wentworth in 2015, had six gains and a single bogey in his round of 66.
Steele had four birdies in a flawless 67, holing putts of 18 and 15 feet on the last two holes to snatch a share of the halfway lead.
Scotland's Martin Laird lies just a single shot behind the leaders.
Laird matched An's five-under-par round, making birdies from close range at the 15th and 17th after starting on the back nine.
The world number 143 then got up-and-down at the long third before finishing with gains from six feet and 11 feet at the eighth and ninth.
"My golf game wasn't very clean," Laird told pgatour.com. "I struggled a little bit with my irons all day but my putting was the best it's been in a long time. A lot of nice saves where you're looking at bogey and roll in a 15-footer for par, so those days are always nice.
"I think I only missed three greens yesterday and today I missed seven or eight greens - so I wasn't quite as tidy tee to green but it's amazing what the putter can do for you when you putt well."
Laird shares third place with first-round leader Matt Kuchar, Korean Sung Kang and Japan's defending champion Hideki Matsuyama.
US Ryder Cup star Rickie Fowler got one of the biggest cheers of the day when he whipped the 20,000 crowd around the 16th into a frenzy before firing a wedge to within a couple of feet, only to then miss his birdie putt.
A round of 68 was enough to give Fowler a place inside the top 10.