The 21-year-old McIlroy, who became the youngest first-round leader in Masters history, posted his score in one of the early groups and then waited in the clubhouse all day to see if anyone could catch him.
No one did until Quiros birdied his final two holes under darkening skies in the last group of the day. It was the long-hitting Spaniard's best result at a Masters, where he had never shot better than a 75.
South Korea's Y.E. Yang and K.J. Choi were two shots back at 67. Nine other players were in the 60s. Defending champ Phil Mickelson scrambled for a 70, and Tiger Woods was within striking distance at 71.
McIlroy, of Northern Ireland, is used to contending in the majors, finishing third at last year's British Open and PGA Championship. He also helped Europe reclaim the Ryder Cup.
“I trusted everything,” McIlroy said. “I trusted where I wanted to hit the ball. That's the key around here. With some of these pins, you can get tentative and try to guide it in there. You just have to pick your targets and trust your swing. I was very happy with the way I did that.” McIlroy nearly duplicated his dynamic start at last year's British Open, where he opened with a 63. The next day at St. Andrews, in a howling wind that actually forced a brief delay, he slumped to an 80.
“At the time, it was very disappointing,” McIlroy said.
“But looking back, it was probably very valuable in my progression as a golfer.” McIlroy fired off three straight birdies Thursday, starting on the par-5 second hole. He then hit a 7-iron just left of the pin on No. 9 and picked up another birdie on the 11th with a 5-iron. Two more birdies followed, but no bogeys.
McIlroy doesn't expect to fall apart on Friday.
“I have that experience to draw on,” he said, “especially being in a similar position to last year at St. Andrews. I feel like I'm better prepared to tee off in the second round of a major with the lead.” Quiros was strong off the tee, but it was his putter that kept him in the game. After driving behind some trees at No. 14, and going even deeper when his next shot struck a limb, he rolled in a 20-foot putt to salvage a bogey.
He made a 25-footer for birdie at the 17th, then stuck his approach shot right behind the flag on the final hole. He rolled in the short birdie putt and had a share of the lead at a place where he's never even made it to the weekend.
“The two previous years, I came to the Masters thinking that I can play well, shoot low. And this was my main mistake,” the 28-year-old said. “It's a golf course. It's too tough. Every single situation has to be measured. I mean, the risk, the reward. And today, I was very happy making pars. This is why probably I shoot 65.” Yang made an eagle at the 13th and briefly pulled into a share of the lead with consecutive birdies on 15 and 16.
But a wild drive behind the trees led to a bogey at the 17th, and the Korean made another on the final hole after knocking his approach shot over the green.
His countryman took a different tact. Choi birdied five of his last six holes, capped off by a brilliant putt at 18 from the front of the green to the pin.
Woods was six shots back, but at least he wasn't totally out of it. Mired in the longest winless streak of his career, he made a long putt at No. 14, lipped out several others and finished with a 71.
“I'd rather be where Rory is,” said Woods, who has gone 20 tournaments over 17 months without a win. “But, hey, there's a long way to go. ... I'm very pleased. I'm right there in the ballgame.” Mickelson, coming off a win at Houston last week, was far more erratic off the tee, hitting shots into the pines and spraying one far into the azaleas left of the 13th. He hit only four fairways, last in the field of 99 players.
He scrambled to save the first of seven straight pars before a birdie at No. 8 pushed him into the red for the first time. On the 18th, he missed a 7-foot putt for his only bogey of the day.
“It was just OK,” he said. “I didn't shoot myself out of it. But I didn't make up ground on the field like I wanted to. So I've got to go do it tomorrow.” Matt Kuchar and Ricky Barnes were at 68, while seven others were in at 69: Sergio Garcia, Charl Schwartzel, Brandt Snedeker, Ross Fisher, Geoff Ogilvy, Gary Woodland and 2008 Masters champion Trevor Immelman.
Two-time US Open winner Retief Goosen had the early lead after holing out an eagle from the fairway on the first hole. But the South African limped to the finish with three straight bogeys for a 70.
US PGA champion Martin Kaymer came in as the world's top-ranked player, but he's never made it to the weekend at Augusta. The German opened with a dismal 78 - his worst score yet in the Masters.
“For me, it was very difficult,” Kaymer said. “There's some golf courses that suit you and some, they just don't.” Lee Westwood, ranked second behind Kaymer and runner-up to Mickelson last year, opened with a 72.
“It's not my game at the moment,” the Englishman said.
“If you can't hole it out from 4 feet, you're going to struggle.”
