The 2013 Masters champion blew a huge chance to win at Royal Lytham a decade ago.
Dustin Johnson set the early clubhouse target after a second-round 67.
Armitage began the day seven shots off the pace following an opening 71.
The 1989 champion, now 62, props up the leaderboard after an opening 83 at St Andrews.
McIlroy is just two strokes behind leader Cameron Young.
Players found themselves waiting for long periods on tee boxes and also for second shots into greens.
The 15-time major winner never recovered from a nightmare start.
America’s Cameron Young held the lead thanks to firing eight birdies in a flawless 64.
Some of Thursday’s rounds took longer than six hours.
The four-time major winner lies just two shots off clubhouse leader Cameron Young at St Andrews.
