Defending champion Jordan Spieth has held the Masters for five consecutive rounds following a bogey-free six-under par 66 in the first round at Augusta National.
Spieth, who led wire to wire last year, has a two-stroke lead over Shane Lowry of Ireland and New Zealand's Danny Lee, each of whom shot 68.
"I got a lot out of the round with what I felt like was kind of average-ish ball-striking," said Spieth. "Just scored the ball extremely well, which is something I've been struggling with this season. I am extremely pleased with that round today. I felt like we stole a few. I put it up there with one of the best rounds I've played, one of the best rounds I've scored."
Rory McIlroy, needing a win at the Masters to complete the career grand slam, shot a two-under par 70. He is tied for 10th and four shots back of the lead.
Jason Day, after getting to five-under par and one shot off the lead through nine holes, finished with an even-par 72. He had three bogeys on the back nine, and a triple bogey on 16. He is tied for 21st, six shots off the lead.
Bubba Watson, a two-time Masters champion, had a difficult time navigating the back nine as well. He had five bogeys and a double bogey on 16, leading to a three-over 75. Watson is nine shots off the lead.
Rickie Fowler, still looking for his first major championship, shot an eight-over 80 in a round that featured four bogeys, two double bogeys and a triple bogey at the par-5 13th hole. He is tied for 81st.
Phil Mickelson, seeking his fourth Masters victory, shot an even-par 72.