Halfway leader Scott riding momentum at Doral

Scott is two shots in front of fellow long-hitters Rory McIlroy and Dustin Johnson.

“There is momentum and it’s a huge factor,” Scott told Golf Channel. “The trick is to figure out how to use it, how to maintain it and keep it going from week to week.

“So far this week I’ve done a good job. Now the weekend is a different animal. The leaderboard looks great. It’s going to be exciting and at the moment the course is producing good scores. I might have to keep it going at this same pace.”

Scott, 35, made eight birdies and two bogeys and said he fed off the terrific play of playing partner Johnson. The American posted the low round of day at 64 thanks to a scorching, five-under tour of the back nine.

“I’ve been playing really well,” said Johnson, who opened with a 72. “I just never really got out of position."

World number three McIlroy required only 23 putts in his second-round 65, using 10 fewer putts than on Thursday.

The Northern Irishman altered his putting grip earlier this week from conventional to left-hand low and the move reaped dividends in the second round.

“It’s felt really comfortable, it really has,” McIlroy said. “I’ve done it before in my rookie season on the European Tour in 2008.

“In my mind it couldn’t have gotten any worse," he said about his putting. "So why not make a change? The change is feeling very comfortable at the minute and I’m willing to stick with it.”

American Phil Mickelson was in the lead at nine-under with four successive birdies from the fifth hole, but he gave those shots back with two bogeys and a double-bogey in his final six holes to register a 72 to sit at five-under tied for seventh with England's Paul Casey.

Englishman Danny Willet was alone in fourth place at seven-under after a 69, one stroke ahead of double Masters winner Bubba Watson and Charley Hoffman.

World number one Jordan Spieth was tied for 12th at three-under after a 72.

(Reporting by Tim Wharnsby; Editing by Larry Fine)