A late double bogey sent Paul Dunne slithering down the leaderboard as world No 1 Dustin Johnson fired a stunning second round 63 to snatch a one-shot lead in the WGC-HSBC Champions in Shanghai.
The Greystones man was inside the top-10, one-under for the day and six-under for the tournament with two holes to play but made a seven at the par-five eighth en route to a second round 73.
As a result, the world No 81 fell 16 places to tied 22nd on four-under, leaving him nine strokes adrift of Johnson, who leads by a shot on 13-under-par from fellow American Brooks Koepka, the US Open champion.
Thailand’s Kiradech Aphibarnrat and England's Justin Rose are three shots further back on nine under par, despite dropping a shot apiece on the 18th hole.
Johnson, who was the champion in Shanghai in 2013, became the first player in history to win each of the four World Golf Championships events when he lifted the trophy at the Dell Technologies Match Play in March.
The 33-year-old began the day four shots off Koepka’s lead, but seven birdies in a back nine 29 - including four in a row from the 15th hole - saw him surge clear of the field.
Koepka fought back with two birdies in his last three holes to sign for a 68 and sit at 11 under par, two shots clear of Aphibarnrat and Rose, who had both shared the lead at times on Friday.
But Johnson's back-nine blitz put him a commanding position - an achievement all the more remarkable considering he only used his putter for the first time shortly before teeing off.
Patrick Reed sits in fifth place at eight under par, while fellow European Tour players Matt Fitzpatrick of England and Sweden’s Henrik Stenson - who finished tied second at Sheshan International Golf Club last season – are one shot further back alongside American pair Matt Kuchar and Brian Harman.
Spain’s Rafa Cabrera Bello, who fired an eagle two on the 16th, and Tyrrell Hatton of England finished the day at six under par.
“Obviously I played very well today. But I actually got a putter like about 20 minutes before I teed off, it's a Spider, so it's one that I've used before.
“I wasn't really pleased with the one I played with yesterday, so the guys here in China made me one. I got it right before I walked to the tee. I hit a few putts on the practise green with it and I was like, oh, this will work pretty well. Went out and holed a lot of putts today, so I kind of like it.
“It's a golf course that I enjoy playing. It suits my eye very well. It's still, though, you've got to drive it well. For me, if I drive it good out here, I feel like I can make a lot of birdies. I can reach all the par fives if I drive it in the fairway. The rest of the holes, I feel like if I'm in the fairway, I can attack the golf course.”
“I was pleased with that. Backed up a solid start and continued some momentum today. It was definitely tougher out there today. To post a good score I'm very, very happy with.
“It was a disappointing way to finish. I felt like I was running out of steam a little bit coming in. I think I got lucky with my tee shot, really, so probably deserved six off the tee, but obviously, it is what it is.
“It was certainly trickier with the iron play to judge the wind and to get the ball close to the hole. So all in all, great couple first days. Put myself in contention for the weekend and we're in a good spot going forward now.”
“Yeah, I’m pretty pleased. I started off the day with a bogey and I came back with a couple of nice birdies. You know, it's a bit of a mixed bag with the long game.
“I've got a few things I'm working on and not really firing on all cylinders. I’m still hitting a number of nice shots out there and I guess the part I've been the most happy with is the putting grip. I've been putting solid both days and made my fair share I think. So that's kind of what keeps the scores together.
“I'm pretty pleased with the first two days, for sure, and we’ll see if we can keep on heading in the right direction.”
WGC-HSBC Champions, Sheshan International Golf Club (par 72)
131 D Johnson (USA) 68 63,
132 B Koepka (USA) 64 68,
135 K Aphibarnrat (Tha) 65 70, J Rose (Eng) 67 68,
136 P Reed (USA) 66 70,
137 B Harman (USA) 68 69, H Stenson (Swe) 68 69, M Fitzpatrick (Eng) 68 69, M Kuchar (USA) 67 70,
138 R Cabrera Bello (Esp) 68 70, T Hatton (Eng) 68 70,
139 G Green (Mas) 65 74, D Berger (USA) 68 71, C Howell Iii (USA) 72 67, D Lipsky (USA) 69 70, M Southgate (Eng) 68 71, P Uihlein (USA) 72 67, S Hend (Aus) 71 68, K Stanley (USA) 71 68, W Ashun (Chn) 67 72, T Finau (USA) 67 72,
140 Paul Dunne (Irl) 67 73, R Fox (Nzl) 71 69, H Porteous (RSA) 66 74,
141 B Wiesberger (Aut) 71 70, T Fleetwood (Eng) 71 70, C Kim (USA) 69 72, P Perez (USA) 72 69,
142 A Levy (Fra) 71 71, P Cantlay (USA) 68 74, S Kim (Kor) 71 71, M Lorenzo-Vera (Fra) 71 71, S Chawrasia (Ind) 72 70, J Smith (Eng) 69 73, L Wenchong (Chn) 72 70, H Ryu (Kor) 69 73, H Tanihara (Jpn) 72 70,
143 C Schwartzel (RSA) 73 70, P Mickelson (USA) 71 72, P Casey (Eng) 71 72, D Kataoka (Jpn) 71 72, J Day (Aus) 69 74, B Grace (RSA) 74 69, J Vegas (Ven) 70 73, R Henley (USA) 75 68, P Saksansin (Tha) 73 70, C Reavie (USA) 69 74, A Hadwin (Can) 69 74,
144 R Ramsay (Sco) 73 71, F Zanotti (Par) 73 71, A Scott (Aus) 72 72, H Swafford (USA) 70 74, B Haas (USA) 71 73, A Noren (Swe) 72 72,
145 A Hall (Aus) 74 71, T Olesen (Den) 72 73, R Sterne (RSA) 73 72, L Yanwei (Chn) 72 73, M Griffin (Aus) 68 77,
146 X Schauffele (USA) 71 75, J Rahm (Esp) 72 74, L Glover (USA) 71 75,
147 P Khongwatmai (Tha) 69 78, R Fisher (Eng) 77 70, D Zecheng (Chn) 71 76,
148 F Molinari (Ita) 77 71, M Hendry (Nzl) 73 75, H Matsuyama (Jpn) 74 74, Z Xinjun (Chn) 71 77, L Haotong (Chn) 72 76,
149 G Storm (Eng) 75 74, W Bryan (USA) 77 72,
150 M Leishman (Aus) 71 79,
151 S Imahira (Jpn) 72 79,
153 A Dodt (Aus) 74 79,
154 T Pieters (Bel) 75 79,
157 C Yi (Chn) 74 83,
165 B Stone (RSA) 78 87