Rory McIlroy of Northern Ireland hits off the 12th tee during second round play of the 2018 Masters golf tournament at the Augusta National Golf Club in Augusta, Georgia, U.S., April 6, 2018. REUTERS/Mike Segar

By Frank Pingue

AUGUSTA, Ga. (Reuters) - Rory McIlroy gave his quest for a career grand slam a boost by grabbing a share of the second round clubhouse lead at the U.S. Masters on Friday while former champion Tiger Woods was flirting with the cutline.

McIlroy, who with a win this week would be only the sixth player to win each of golf's four majors, shot a one-under par 71 on a tough scoring day at windy Augusta National that brought him to four under for the tournament.

"A little disappointed walking off the 18th green. I had two good chances on 17 and 18 that I didn't convert, but overall, 71 out there today was a pretty good score and obviously in a nice position going into the weekend," said McIlroy.

The 28-year-old Northern Irishman was joined atop the leaderboard by former champion Jordan Spieth (74), whose two back-nine birdies helped erase some of the damage caused after a rough start that included a double-bogey at the first.

McIlroy and Spieth were one shot clear of world number one Dustin Johnson, who birdied the last to reach the clubhouse at four-under par 68.

A further shot off the pace were 2017 runner-up Justin Rose (70), Rickie Fowler (72) Masters rookie Tony Finau (74) and South African Louis Oosthuizen (71).

Still on the course was leader Patrick Reed, who was eight-under for the tournament after a sizzling opening nine holes that included six birdies and one bogey.

Woods fell to four over par after a rough front nine that included a bogey and double-bogey and left him sitting one shot inside the cutline, which is projected to be five over par.

The former world number one was considered a favorite to collect a fifth Green Jacket after showing impressive form this year in his comeback from injury but had nothing going his way early in his second round.

After a bogey at the opening hole, Woods made a double-bogey at the par-four fifth hole where he took a penalty drop from an unplayable lie after sending his second shot into the bushes to the left of the green.

Sitting right on the projected cutline is three-times winner Phil Mickelson who had a triple-bogey, double-bogey, four bogeys and two birdies for a seven-over-par 79.

Sergio Garcia, whose 81 on Thursday was the worst opening-round score by a defending champion, was unlikely to make it to the weekend as he was two over through his first nine holes on Friday.

(Reporting by Frank Pingue, editing by Pritha Sarkar)