Rory McIlroy suffered another final round reverse as his driver let him down and he failed to raise a gallop in the Farmers Insurance Open at Torrey Pines.

Tied for eighth overnight, three shots behind Patrick Reed and Mexico’s Carlos Ortiz, the world No 7 could only manage a final round 73, finishing tied 16th on six-under - eight shots behind Reed who shot a 68 to win by five..

The Co Down man turned in two-under but missed a three-footer for par at the 10th, then bogeyed the par-five 13th after bunkering a tee shot to fall six strokes off the pace.

Putting held McIlroy back during the first three rounds but needing a solid foundation from the tee to mount an early final round challenge, he didn’t hit a fairway until the sixth and found just six in total, leaving him 48th for strokes gained off the tee in the final round compared to first and T13th on days one and three.

Even when he birdied the 14th thanks to a 322-yard missile from the tee, he immediately double-bogeyed the 479-yard 15th, flaring his drive 50 yards right of the centre of the fairway from where he overshot the green, chipped to 33 feet and promptly three-putted.

He salvaged par from 15 feet at the 17th despite being forced to take a penalty drop after driving into the hazard left, but again missed the fairway at the 18th and finished with a par-five.

Reed, in contrast, raced away from the field with another impressive short game display, shrugging off the rules controversy surrounding his drop for an imbedded ball at the 10th on Saturday.

Before the round, McIlroy and Reed were both cleared of any wrongdoing after both took relief from embedded balls in the rough — Reed at the 10th and McIlroy at the 18th—during Saturday’s third round.

The PGA Tour’s signalling of McIlroy was clearly intended to deflect attention from Reed but social media was having none of it.

Reed was at the centre of a social media storm on Saturday evening after video of his ball bouncing on impact was widely circulated before he began examining his ball in the rough at close range.

He removed it and called a referee, leading some to argue that he had self-embedded it.

It later emerged that McIlroy got a similar drop at the par-five finishing hole, promoting the PGA Tour to issue a statement on the rulings yesterday.

“It was reasonable for both players to conclude - based on the fact that they did not see the ball land, but given the lie of the ball in soft course conditions - that they proceed as the Rule allows,” the PGA Tour said.

“Both players took proper relief under the Rule 16/3. The Committee is comfortable with how both players proceeded given the fact that they used the evidence they had at the time.”

McIlroy insisted he’d never tried to take advantage of the rules and did not believe that players were becoming too cavalier in relation to them.

“I don't think I've ever had an issue before with the rules, or if I have, it's been a long time,” he said. “I remember my first trip at Augusta with the bunker on 18 back in '09. But look, like everyone out here, it's the worst thing in golf to be labelled as someone that tries to get away with something or labelled a cheater and that's just not how you want your reputation to be.

“Even going back to the PGA Championship at Harding Park last year, I got relief because someone stepped on my ball, but I didn't feel right because the lie that I had was way worse than the lie that I would have been given. So I gave myself a worse lie to just try to be fair to the field and the tournament in general.

“I've never tried to get away with anything out here. I think I said at the time, you know, in golf you'd rather be on the wrong side of the rules than the right side of them just to -- because that's just what our game's about. Our game is about integrity and it's about doing the right thing. I always try to do the right thing and hopefully people see that. I feel like I have a reputation of that.”

As for his performance, he pointed to his putting over the first three days as the main cause of his failure to win.

“Yeah, I'm looking forward to getting on some truer greens,” he said of his appearance at this week’s Waste Management Open. “As the poa gets soft here, obviously it gets a little bumpy and you start to just make some really tentative strokes and I sort of started to do that over the weekend here.

“Obviously it was a disappointing finish. I wish I had -- I got it to 9 under early and then seeing where 9 under is now, I think it's tied second at the minute, those three shots I dropped on the back nine were pretty costly. Yeah, again, I'm seeing some good signs in my golf, but still, some things I need to work on.”