Rory McIlroy went backwards after a rare off day from tee to green but Graeme McDowell dug deep to lie just two shot behind Bubba Watson on a packed leaderboard at the Genesis Open.

The top 15 players are covered by just five strokes at Riviera Country Club, where left-hander Watson shot a six-under 65 to lead by a stroke on 10-under par from Patrick Cantlay, who made an outrageous 54-footer for birdie at the 18th in a grinding 69.

McDowell hit just seven fairways compared to 10 and 11 on the first two days, but he's third for scrambling after getting up and down six times out of eight on a low scoring day in Los Angeles.

With the Tour softening the greens a touch, the scoring average was 70.60 compared to 72.13 on Friday and 72.20 on Thursday. Scores

McIlroy shot a two-over 73, his challenge ending when he had to reload on the 12th and took six before dropping another shot after another pulled tee shot at the 15th to share 42nd on level par.

World No 1 Dustin Johnson, the defending champion, made a big move as he covered his homeward nine (the front nine) in six under 29 for a stunning 64 that leaves him just three off the lead in a tie for eighth on seven-under.

McDowell had enough with a one-under 70 to share third with the bogey-free Australian Cameron Smith, local favourite Kevin Na and big-hitting Tony Finau on eight-under par.

Chasing his fourth PGA Tour win and his first since 2015, he combined birdies at the second (22ft from off the green), 11th (10ft) and 17th (5ft) with bogeys at the par-three fourth and 16th before avoiding a three-putt from 12 feet at the last by solidly drilling home a six-footer after the excitement of Cantlay's long bomb.

It was an important mental test for the Portrush man, who has struggled to play consistently for four days in a row and while a win would put him in the Masters and catapult him as high as 64th in the world, he's not getting ahead of himself.

World No 117 Watson hasn't won since he claimed the second of this two Riviera wins in 2016 but he made just one bogey in his 65 and can join Arnold Palmer, Ben Hogan, Lloyd Mangrum and Macdonald Smith as the only people to win the tournament three or more times.

“The tougher the golf course, the more focus I have,” Watson explained.

“The tougher the difficulty of the shot, I've been able to focus better. When I get my mind on something, I can focus and do pretty well at the game of golf.”

Derek Fathauer is tied seventh, just three behind Watson with Dustin Johnson now a factor in joint eighth after his 64, tied with Justin Thomas, Aaron Baddeley, Scott Stallings and Ryan Moore.
 
“I made a slight adjustment on the range this morning, I just got a little bit closer to the ball,” Johnson said.

“I started hitting it more out of the middle of the face, seeing the shape that I wanted to, and I just played really solid all day today, hit a lot of really good shots.”

Jordan Spieth shot 69 and lies seven behind on three under and admits he finds Riviera a tough test mentally.

“I'll either finish I think third at best and anywhere from third to 25th because I'm just, I'm not quite patient enough to play this golf course,” he said

“I really need to approach it a lot like I approach Augusta. It has a lot of similarities in the way you have to attack it… centre of the green is fantastic. You can putt to any pin from the centre of the green and wait for your chances.”

It's interesting that McIlroy has dismissed that Augusta theory - one of Jack Nicklaus' great adages - as irrelevant in the age of super-fast greens.

McDowell missed a few chances yesterday but knows that with a good result today and some good form over the next few months, he can perhaps start to think about the Ryder Cup again.

As a two-time Open de France winner, he knows that skipper Thomas Bjorn will be keeping an eye on him if he can put a string of performances together and get himself close to the qualifying places towards the middle of the summer.

As for Pádraig Harrington, a potential Ryder Cup captain in 2020 or 2022,  he posted a level par 71 to move up 10 places to 64th on two-over.