AUGUSTA, Ga. — No nerves. No worries. Adam Scott never knew the opening round at the Masters could be so enjoyable. With his green jacket upstairs in the locker room for Masters champions, Scott made only one bad swing that cost him two shots in an opening round of 3-under 69 Thursday at Augusta National. It was the lowest opening score by a defending champion in 13 years and left Scott one shot behind leader Bill Haas on an otherwise demanding day. "It was really how you hope to come out and play at any major, and especially the Masters," Scott said. "And there's no doubt winning the Masters last year had me a little more comfortable on the first tee than I've ever been in the past because I didn't have the legs shaking and nerves jangling for six or seven holes like usual." Haas — who has a rich family history at Augusta that includes a green jacket for great uncle Bob Goalby — settled down after an opening bogey with a collection of good birdie putts and an 8-iron to 5 feet for birdie on the 18th for 68.It was the first time in 18 majors that Haas led after any round. That gets him only a crystal vase for the low round of the day at the Masters. Haas knows better than to put too much stock into what happens Thursday. He led after the opening round of the Houston Open last week and finished tied for 37th. "There's tons of golf left," Haas said.At the previous 77 Masters, the winners held the outright first-round lead only nine times. Only once in the past 29 years did the winner hold at least a share of the lead (Trevor Immelman shared it in 2008).Haas' father, Jay, played in 22 Masters, making 19 cuts. Uncle Jerry Haas participated in 1985. An uncle on his mother's side, Dillard Pruitt, played the Masters in 1992 and '93.Goalby won the 1968 event, avoiding a playoff after Roberto De Vicenzo signed for the wrong Sunday score. Bill Haas, 31, said Goalby encourages him by saying, "You're a better player than the scores you shoot."Scott was at 3 under with 2012 Masters winner Bubba Watson, who had the day's only bogey-free round, and Louis Oosthuizen, who lost to Watson in a playoff two years ago.They were the only players to break 70, the fewest for a Masters opening round since 2007.Two-time major winner Rory McIlroy, a favorite to win his first Masters, thought the course was playing tougher than a normal Masters on Thursday. "I think anything under par was a good score. They set the golf course up very difficult for a Thursday," said McIlroy, who shot 1-under 71, same as playing partner Jordan Spieth. Augusta National officials knew the weather would be gentle, and they made sure the course was anything but. The hole locations were severe for an opening round. With endless sunshine, the greens became firmer and quicker by the hour.Many paid the price. Jason Dufner took quadruple-bogey 9 on the 13th with only one penalty shot. He wound up with 80 in his first round in a major since winning the PGA Championship last year. Phil Mickelson had a pair of 7s on his card for the first time in five years at a major (Round 3 at the 1997 PGA Championship), and his 76 matched the highest opening round at Augusta for the three-time champion (the other was in 1997, the only year he has missed the cut).Defending U.S. Open champion Justin Rose shot 40 on the front nine and scrambled for 76. Jason Day had 75 in his first event in six weeks. Luke Donald shot 7-over 79, his highest score at the Masters, and it included a two-stroke penalty on No. 9. Information from ESPN, cbssports.com and the PGA Tour was used in this report.