Overnight rain took the sting out of Riviera but Rory McIlroy still had to produce a solid performance on the greens to open with a four under 67 in the Northern Trust Open as Jordan Spieth suffered a rare meltdown and crashed to a 79.

The world No 3 finished the day four shots behind Camilo Villegas in joint fifth, dropping just one stroke on his debut in the event as Bubba Watson, Chez Reavie and Luke List shot 66s and world No 1 Spieth's overall imploded, taking 34 putts and hitting just nine greens in regulation for a 79 that left him joint last with John Huh in the 144-strong field on eight over.

Spieth three-putted the third and sixth to go two over, birdied the seventh from 18 feet but would pick up just one more shot at the 10th on a day to forget.

Missed fairways and greens at the eighth and ninth led to two more bogeys and a outward three over 38. And it got worse on the back nine as he followed that chip and putt birdie at the 10th with bogeys at the 12th, 13th, 15th and 16th, capped off by a three-putt double bogey at the 18th.

Despite it all, he took it on the chin, remarking: "I felt like there were a couple of rounds last week where I shot two under and I was more miserable than I was today. It's a day that's one in hopefully, every couple of years.

"I've shot 80 on tour, I've shot in the 80s a couple of times on tour. I think I shot 79 today on a par 71. So in the course of a career, I imagine it is going to happen. Just unfortunate when it actually does.

"It's amazing. I feel really confident about where my game is, and had a great range session, Cameron is here, and there was nothing pinpointed that was wrong. I just played really poorly from good positions off the tee, and didn't strike the iron shots bad either. I just overdrew it when you can't be left and I overcut it when you can't be right. Just bad timing."

The changed condition of the course proved too much for Spieth to compute and he admitted he struggles on soft, poa annua greens.

"So just had a really tough time trusting the way that the course conditions were, and that certainly wasn't all of it, but that was a good amount of it to start with some in-between numbers and just seemed to be anywhere you really shouldn't go, I went, and again, it's just a day to forget, and I won't think much on it.

"I'll come out tomorrow -- I'm not throwing this tournament away. I believe that I can shoot 10-under par on this golf course. There's a 9-under round right now, and I think I can do that. I'm not packing it in by any means.

"I was just very surprised when I looked up on some of the iron shots. I felt like I put good swings on them and I looked up and all of a sudden, they were further off-line.

"Like the one on 18, that one, it was an in between number and so I played probably the wrong shot. I should have hit a 7-iron into the front centre of the green and made par, but why wouldn't I try and birdie at this point, right. I mean, I need birdies.

"And I look up and I think that the ball is going to be fading toward the hole the way I strike it, and it's not. So no, I didn't expect things to go poorly. I actually expected something to go in. But then when you start getting these 5-, 6-footers on softer poa annua, that's where I really struggle. It certainly showed today."

It was the worst putting performance and opening round of Spieth's PGA Tour career but it turned out to be one of McIlroy's better days on the testing greens while he was solid from tee to green on a course that is notoriously demanding for even the great ball-strikers.

"It was a solid round of golf, first time here competitively and there were a few opportunities on the back nine, our first nine, that I managed to take advantage of a few and turned in a couple under," McIlroy said after taking just 27 putts.

"I played a solid front nine, which I feel is the harder of the two nines. But the course played a lot different today to what I experienced on Tuesday and Wednesday. It was a lot softer and it played a lot differently, so you had to adjust to that a little.

"I feel that helped me somewhat, being able to control my irons into greens and not going that far whenever it hit.

"I felt like I did okay on the greens for the most part. On the eighth hole, it was right in the middle with three feet to go it hit something and missed on the right edge. Apart from that I felt like I putted pretty well. My pace was good, which I was happy with. The ball can get away from you on these greens, especially putting towards the ocean.

"So I felt like my putting was good and my lag putting was good as well. I left myself a lot of putts from 40-50 feet that I got close with good two putts and took advantage of a few of the chances I gave myself. A 67 is a pretty decent start. "

Pádraig Harrington three putted twice and racked up 34 putts in total as he mixed two birdies with two bogeys for a level par 71 that was just inside the cut line early in the day.

But while nothing dropped, it was at least a positive ball striking day for Harrington, who unusually hit 16 of 18 greens in regulation

Starting on the back nine, McIlroy birdied the short, par-four 10th  from six feet and picked up another shot the par-five 11th, shaving the hole with a 73 footer at the latter after two huge hits in the damp, overcast, early conditions.

Asked his approach to the 315-yard 10th, he told PGA Tour Radio: "Left. I don't care. You can hit it as far left as you want and take bogey out of play anyway. You will always have a shot from left and even from watching this tournament over the years, that's all I knew. Just hit it left and try and get it somewhere green high and you can try and chip up the green.

"So I will be trying to do the same thing all week. I hit three wood off the tee today and hit a good tee shot and was pin high left and made the putt." 

His only dropped shot of the day came at the 15th, when he lost his tee shot right into a trap and then failed with a 12 footer for par having done well to blast out some  45 yards short and left of the green.

But as the day brightened up, McIlroy's biggest challenge was spin control into the sticky greens, which had been firm and releasing earlier in the week until the heavens opened in the early hours of Thursday.

Forced to chip and putt for par after spinning an eight iron off the front of the 16th, McIlroy drove into sand at the 590-yard 17th but recovered with a good lay up, a super third to nine feet and a perfect putt.

He burned the edge with a 20 footer for birdie at the 18th but quickly moved to three under with a two-putt birder from 35 feet at the easy first.

He had to hole a seven footer for par at the second after coming up short in two and a five footer for another par at the third after getting a flyer through the back from the left rough. 

Another single putt followed at the testing, 234-yard fourth, where he came up just short of the green and while he missed chances for birdie from 16ft, 11ft and 12ft at the fifth, sixth and eighth, he birdied the seventh thanks to a 143 yard approach to three feet.

He had another chance to birdie the last but spun his 130 yard approach off the green into the rough and did well to steer home a slippery, four footer for a closing par.

He admitted the overnight rain helped him, adding: "It was fast and firm on Tuesday and Wednesday and obviously the overnight rain changed the characteristics of the golf course a lot and that was something we needed to adjust to today. If anything, it actually made the golf course a little bit easier so I am happy with 67.

"I felt like I played very much within myself most of the day, took advantage of a couple of opportunities and played the par-fives well."