"One of the reasons why I'm playing less tournaments this year is that I can hopefully prolong my career and be out here for a little bit longer".
2014 victor McIlroy endured as bad as a start as he has ever had to a Major, hooking his first tee shot out of bounds en route to a double-bogey on the first hole - and it didn't get much better from that point onwards.
The three-time major victor, still only 25, moved his name up the leaderboard at the British Open on Friday with a superb four-hole run near the end of the front nine. "And I'll dust myself off and come back out tomorrow and try to do better". It's like, 'Well, I can't really start much worse than this, may as well just keep the head down and keep going.' I thought I showed some resilience around the middle of the round.
McIlroy had an unplayable lie, so he took a drop and therefore was hitting six.
McIlroy's first tee shot went out of bounds and he started with a quadruple-bogey eight.
There were cheers elsewhere on the Dunluce links early on as another Northern Irishman Darren Clarke, who hit the opening shot of the tournament, started brightly before hitting two bogeys in the final three holes for an even-par round of 71.
The intensity of his play was in stark contrast to Mickelson's, the American taking an ugly double-bogey on two after twice seeing chips from a valley short left of the green roll back down to his feet.
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After carding an 8 on the opening hole, McIlroy made another bogey on No. 3 before birdieing the seventh and ninth holes for three-over 39 on the front.
Argentina's Emiliano Grillo got the crowds excited with the first hole-in-one at the championship since 2016 on the par-three 13th. He missed a 4-footer for par and then slapped and missed a 1-footer for bogey. He was left of the green on the par-5 second, which looked like a simple up-and-down for birdie until his putt barely reached the green.
"On 18, I hit a tee shot that I knew wasn't going to be in the fairway, but I didn't think it was going to be quite as bad as it was", McIlroy said.
The three-time Open champion hit a hybrid off the first tee into the left rough, beginning a round that will determine whether he plays on the weekend.
"It was obviously a disappointing day", McIlroy said.
"To be honest I've been struggling lately and this is the first day it's felt pretty decent, ball striking-wise".
Asked about the enormous support he will receive over the weekend, the 32-year-old from Offaly added: "Next week I'l be in Memphis and there'll probably be 10 men and a dog following me".