Caddies' numbers on the front of their white boiler suits represent the figure given to each player as they compete at the Masters.
And the reason behind each number is simple - it is the order in which they registered when arriving at Augusta National. This means, at 89, McIlroy was the very last player to register himself this year.
The Northern Irishman arrived on Tuesday after competing at the Valero Texas Open last weekend. He then spent a day back at home in Jupiter Island, Florida, before jetting up to Georgia. In fact, he went straight into a press conference after arriving and made that point clear.
"I just drove in probably 30 minutes ago," he said before adding how he plans to treat this week. "If I cast my mind back to 18-year-old Rory and I'm driving down Magnolia Lane for the first time, how would I feel and I think, it's just always trying to go back to being grateful and feeling incredibly lucky that you can be a part of this tournament and you get to compete in it every year."
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There is, however, one exception to the rule; the first person to arrive does not get the No.1. That honour goes to Jon Rahm and his caddie for winning the 2023 tournament. It means whoever arrives first, unless it is in fact the past winner, will get No.2.
This year it was Jason Day. The Australian arrived Friday and was spotted practicing before and over the weekend in a bid to get ahead of the game. The second person to arrive was Jose Maria Olazabal (No.3), with the third Luke List (No.4).
Caddies then wear the number on the front left of their white boiler suits with the player's name clearly emblazoned on the back in capitals. And the reason why the caddies are all in white is to simply help them stand out more.
McIlroy carded a solid 1-under round on Thursday to begin his 2024 Masters campaign. This year's 89 had to battle through tough conditions, with gusts up to 20mph, but was still listed his errors and felt he could have done better.
The conditions are tricky," he said. "Hard to fully commit to shots out there at times just because the wind is -- if it's across, it feels down at one point and then into. It's hard to commit to where the wind direction is at times.
But yeah, I think after the slow start sort of making a few birdies around the turn was good. A little wasteful coming in. I had a good chance for birdie on 15 in the middle of the fairway and didn't take that. Missed a shortish one on 16 and then the bogey on 17. Probably turned a 3-under into a 1-under there at the end. But overall still not a bad score, and obviously a lot of golf left to play."