Augusta, United States (AFP) — Jordan Spieth threatened to run away with his second consecutive Masters crown before stumbling twice on the front nine and reaching the turn with only a three-shot lead over Rory McIlroy in Friday’s second round at windy Augusta National.

The 22-year-old American, who won last year’s US Open and Masters, stood on six-under-par overall with nine holes to play, one-over on the round after a bogey at nine and a double-bogey blip at the par-4 fifth.

“It depends on how Jordan is going,” said Australia’s top-ranked Jason Day. “He seems to love this course and love this place. It depends on what he does.”

Giving hope to a chasing pack that struggled in vain to gain ground on the 18-hole leader was McIlroy, who seeks a victory to complete a career Grand Slam.

He was two-over through 12 holes but birdied the par-5 13th and 15th and par-3 16th to seize sole possession of second.

“He’s a phenomenal talent and it’s my job and Jason’s job and everyone else’s to try to stop him dominating,” McIlroy said of Spieth on Tuesday.

Spieth is trying to join Tiger Woods, Jack Nicklaus and Nick Faldo as the only players to win the Masters two years in a row.

He would also overtake Day for world number one with a Masters win if the Aussie finishes outside the top five. Day struggled in the wind to fire one-over 73 Friday and stand on one-over 145 overall.

“One-over is probably par for us,” Day said. “I felt like I did all right but it’s just tough out there. It’s really tricky. At Amen Corner (holes 11-13) you don’t know where the wind is coming from.

“It almost feels like a US Open where you have just got to survive. I’m just trying to survive right now.”

South Korean-born New Zealander Danny Lee and American Scott Piercy shared the clubhouse lead at two-under 142 for 36 holes.

Lee fired a 74 Friday, closing bogey-bogey to fall back, while Piercy shot 72, unable to make a run after birdies on two of the first three holes.

“It’s just blowing so hard,” Piercy said. “The wind is playing a huge part. The greens are starting to dry out. If you get them downwind, it’s hard to stop the ball. Even par goes a long ways today.”

No Kiwi has won a US event since Michael Campbell captured the 2005 US Open.

Spieth’s playing partners, US amateur Bryson DeChambeau and England’s Paul Casey, were on the course at two-under.

Spieth, who fired a six-under par 66 in round one, sank a 14-foot birdie putt at the first hole and put his approach two feet from the cup at the third to set up another birdie.

The Texan four-putted the fifth green, missing from four and seven feet to fall back to six-under, and he needed to sink a 17-foot putt just to save par at the par-3 sixth.

Spieth answered with a nine-foot birdie putt at the par-5 eighth but his third shot rolled off the front of the green at nine, leading to a bogey.

Ernie Els, the 46-year-old South African who fired the worst score ever recorded on the first hole, with a nine in round one, managed a double-bogey six at the first on his way to a 73 in the second round.

The four-time major champion sent his approach at the first way left onto the adjacent ninth hole, punched the ball onto the green 47 feet shy of the cup.

He missed his long par putt, then knocked a two-footer past the hole before sinking a comeback four-footer.

Eight-time major champion Tom Watson appeared set to miss the cut in what would be the final round of his legendary career.

The 66-year-old American was six-over with eight holes to play, likely needing multiple birdies to become the oldest player to make the cut in Masters history and extend his career by 36 holes.

Others set to miss the cut were two-time Masters champion Bubba Watson, fellow American Rickie Fowler and South Africans Els and Charl Schwartzel.