SHANE LOWRY insisted he must pick himself up and realise he's playing the best golf of his life as he goes out in the penultimate group in the Masters today.

The Offaly man was bitterly disappointed after he got off to a great start but then dropped three shots in his last 10 holes and carded a 73 to fall seven shots behind Scottie Scheffler at Augusta National.

At two-under-par, he's tied for fourth with Charl Schwartzel and out in the second-last group with Sungjae Im as Sheffler's 71 gave him a three-shot lead over Australian Cameron Smith, who fired a warning shot across the leader's bows with a sensational 68 - the best score of the day by two strokes.

"I don't really know what to say," said Lowry, who shocked TV viewers with his sarcastic "congratulations to caddie Brian "Bo" Martin for a botched lay-up yardage on the 13th and went on to three-putt for bogey. "I'm obviously very disappointed. As you can see from the score, it was tough. There's not many low scores. There's not many good scores. 

"I don't even know what to say. I'm disappointed in myself for that last ten holes that I just had. Yeah, I've just got to pick myself up and go again tomorrow."

Lowry birdied the second and made a 16 footer at the sixth to close to within four shots of Scheffler on five-under but bogeyed the ninth after coming up short of the green with his approach, then followed that six at the 13th with another dropped shot following a bunkered approach to the 17th.

"I just hit a few bad shots," Lowry said. "Like nine, like geez. I was feeling great about my game. Honestly, first tee, no nerves, nothing. I felt so comfortable out there, and that just seemed to kill all the momentum that I had.

"You know, I had just lipped out on eight for birdie, feeling really good, and 99 yards to the flag, I mean, most stupidest shot I've hit in a while. You just can't do that if you want to win tournaments like this.

"Yeah, look, I'm just quite disappointed at the moment. I'll have to pick myself up and get at it tomorrow. Scottie looks like he's in trouble on the last; he could make at least bogey. I'll probably be six or seven back. Tomorrow is supposed to be nice weather. Hopefully, I can go low tomorrow."

Lowry was quick to remind himself he's still in the tournament and with lighter winds and higher temperatures forecast, a closing 65 may still give him a chance.

"It's hard," he said of his disappointment. "I'm playing the best golf I've ever played, and how many times do I get a chance to play the best golf I've ever played at Augusta in the Masters?

"I was quite bullish about my game going out there today and felt ready to take on Scottie and I just didn't do it. The last ten holes just weren't good enough, and it's unfortunate."

He knows he can't force a low score and will have to display more patience than he showed his caddie in that unfortunate rant on the 13th that was picked up on the broadcast.

"I think I just have to play my own game and try to finish as best I can," he said. "There's no point in going out there and standing up and hitting a seven-iron straight at the flag on the first because that's not going to work around Augusta.

"You just need to play your game plan and plod my way around the course like I've been doing and see where it leaves me at the end of the day.

"To be honest, I haven't looked at the forecast, but I do believe it's better. Augusta, I would imagine, there will be a few easier pins. That's what they like to do, I think, on Sundays.

"Look, I've never been in this position at Augusta, so it's the first time for me. I'm happy with that this week, that I've given myself -- you know, been up there this week.

"What's possible, there's a 65 out there in good conditions, but it just depends what the other guys ahead of me do."

Rory McIlroy will go into the final round tied for ninth on one-over after his third round 71, 10 shots behind Scheffler on one-over-par as he partners Collin Morikawa.

Séamus Power's third successive 74 left him 15 shots off the lead on six-over and paired with Australian Marc Leishman for the second day running.