Jordan Spieth's defence of the green jacket got off to a perfect start on Thursday as he ended the first round of The Masters with a two-shot lead at Augusta National.

The 22-year-old, who is looking to become the fourth golfer - behind Jack Nicklaus, Nick Faldo and Tiger Woods - to win back-to-back Masters titles, carded a bogey-free six-under-par 66, shooting six birdies.

Spieth, whose worst score in nine rounds at Augusta is level par, had a comfortable round, but he is under early pressure from New Zealand's Danny Lee and Irishman Shane Lowry, both of whom are two shots behind the top spot.

Five golfers, including Sergio Garcia, Ian Poulter and Justin Rose, are three-under-par in the field, while Rory McIlroy, who is hunting for a career Grand Slam, is four shots behind.

The world number three was two-under at the turn, but his round took a hit when he suffered a bogey on the 11th hole and a double bogey on the 13th.

McIlroy was four-under with three to play, but he had a bogey on the 16th and 18th holes, pushing him back to two-under-par for the day.

World number one Jason Day started strongly and was five-under after 14 holes, but he crumbled and fell to tied-21st in the field after finishing the round on even par.

The Australian, who was runner-up at The Masters in 2011, failed to recover from a bogey on the 15th hole as he triple-bogeyed the next one and suffered another bogey on the 18th.

Ernie Els had a disastrous round as he six-putted the first hole for nine, while Rickie Fowler lingers at the back of the field after carding an eight-over-par 80.