But he still had reason to celebrate at Carnoustie.
McIlroy easily made the cut at 2-over 144. And he can count on being on the 18th green Sunday afternoon for the trophy presentation. He is guaranteed to win the silver medal as the low amateur as the only one of five to make the cut.
'Just to play the weekend at the Open is fantastic,' he said. 'Hopefully, I can enjoy the next couple of days and play some good golf.'
He opened with a 68, one shot better than Tiger Woods and the only player at Carnoustie without a bogey on his card. But the second round soon became a struggle, especially the double bogey on No. 9 with a shot out-of-bounds.
Unchanged was his attitude.
'I just wanted to go out there and try my best, play golf and enjoy it, and that is what I did today,' said McIlroy, who qualified as the European Amateur champion. 'I didn't get upset with bad shots.'
He made his first bogey of the tournament at the par-4 second, firing his tee shot into heavy rough, then landing in a bunker. After the double bogey at No. 9 gave him a 39 on the front side, he dropped shots on the 11th and 12th.
McIlroy was a virtual unknown arriving at Carnoustie. He won the European Amateur title in Milan a year ago after various domestic successes in Ireland. He has played only three European Tour events, tying for 52nd in the prestigious Dubai Desert Classic and missing the cut at tournaments in Portugal and Spain.
Some 70 followers from his local club joined his parents and girlfriend to follow the early stages of his British Open challenge, and they were joined hole by hole by hundreds more spectators.
'The interest has been pretty big,' McIlroy said. 'There were a lot of TV cameras following me and it was nice to play in front of crowds like that. ... I wasn't too nervous today. I was probably more pumped up than nervous.'