Paul Dunne was left to rue a late slip-up at the end of his second round as he dropped down the leaderboard at the WGC-HSBC Champions tournament in Shanghai.
A double-bogey seven on the seventh hole, his 16th, saw him fall to nine shots off the lead held by Dustin Johnson on 13 under.
The Wicklow man was one under par for his round to that point.
He signed for a 73 and sits in a tie for 21st, 15 places down from his overnight standing.
World number one Johnson reaped magic from a new putter to card a sparkling nine-under 63 and take a one-shot lead at the halfway mark.
Bidding for his third World Golf Championships title of the year, Johnson moved to a 13-under total of 131, one in front of overnight leader Brooks Koepka with Justin Rose four strokes off the lead on nine-under, joint third with Kiradech Aphibarnrat.
Disappointed with his work on the greens during an opening round of 68, Johnson grabbed a fresh putter and, after just 20 minutes of practice, put it to brilliant use on the back nine at Sheshan Golf Club.
Four behind at the start of the day, the rangy American rolled in seven birdies after the turn, including four in succession on his last four holes.
"Obviously I played very well today, I actually got a putter about 20 minutes before I teed off," the 2016 U.S. Open winner said after his bogey-free round.
"I wasn't really pleased with the one I played with yesterday.
"I was coming from the range when I grabbed (the new one). I had a few putts on the practice green ... and then I came out and holed a few putts."
After opening with two straight birdies, US Open champion Koepka laboured through a frustrating run of 13 straight pars before breaking the birdie drought on the par-four 16th.
Another birdie on 17 gave him the chance to reel in Johnson on the par-five 18th but he had to be content with a closing par after burning the edge of the cup with a putt from six feet.
Henrik Stenson remains in contention after shooting a 69. The Swede sits six strokes behind Johnson and level with Matt Kuchar (70) in a group of four on seven-under.
Former world number one Jason Day, however, endured a torrid 74 littered with five bogeys and is 12 off the pace on one-under with Phil Mickelson (72).
Hideki Matsuyama's title defence appears all but over after the Japanese carded a second straight 74.