Pádraig Harrington slumped to a disappointing four over 75 as Darren Clarke opened with a 78 and promptly withdrew from the Northern Trust Open with a chest muscle strain at a demanding Rivera Country Club in Los Angeles.

Leaderboard

As Dustin Johnson conquered firm and fast conditions to post an impressive, five under 66 to lead by a stroke in the clubhouse from a group of 11 players when play was suspended due to darkness, the Irish pair suffered mercilessly at the storied Pacific Palisades track.

Neither man putted well, both using the blade 32 times with Harrington three-putting twice and Clarke suffering the frustration of a four-putt at his fifth hole of the day en route to a 78.

He withdrew shortly after signing his card, citing a recurrence of the chest muscle injury that forced him to pull out shortly before what would have been his 500th European Tour start at the Qatar Masters three weeks ago.

He wasn't the only one suffering chest pains on a tough course that demanded utter precision.

Harrington got off to an ideal start, holing a 25 footer for a birdie four at the first and a 10 footer at the third to get to two under.

Sadly, he didn't make another birdie until he drained a tough 17 footer across the 18th green for his 75 at provisionally left him tied for 120th.

In between, it was another forgettable day on and around the greens for a player who has struggled to regain his short game dominance since the ban on square grooves came into force.

His slide down the leaderboard began when he took three to get down from the rough right of the tough, 236-yard fourth before dropping three shots in a row before the turn.

At the seventh, he knocked his 40 foot pitch 11 feet past before being forced to take a penalty drop off his tee shot at the eighth.

He then missed the ninth fairway right and after chipping just inside five feet, he missed the par putt and turned in 37.

Three more shots went — two of them through three-putts — before he rescued a stroke at the last.

After failing to make birdie at the 10th, where he had an 18-yard pitch over the right hand bunker for his second, he pulled his approach to the par-five 11th and failed to get up and down for birdie there too.

Bogeys then followed at the 12th - his tee shot came down 214 yards from the tee in the right rough - and the 13th, where he found the left rough off the tee and three putted from 70 feet, missing a four and a half footer.

He did get up and down at the 15th, but that was for par after coming up 40 yards short with his approach.

Bunkered off the tee at the par-five 17th, he eventually gave himself a 10 footer for birdie but knocked it three and a half feet past and missed the return to pencil in another bogey.

Clarke started on the tough back nine and dropped four shots in four holes in the middle on that nine.

A bad drive cost him a bogey before he four-putted the par-three 14th from nearly 60 feet - he left the first one 10 feet short and knocked the next one four feet past before missing again.

Another shot went after a pushed drive stopped him making the green at the 15th and while he curled in a 16-footer for a two at the 16th, he bogeyed the 18th to turn in 40 and came back in 38.

A birdie at the easy par-five first was followed by bogeys at the second, fourth, fifth and seventh though he did hole a good eight footer for par at the ninth.

Mistakes off the tee were costly for the two former Open champions. Clarke hit just seven of 14 fairways while Harrington hit just one more.

As a result, they failed to hit many greens — Harrington managed just nine but it was still one more than Clarke.