AKRON, Ohio — Rory McIlroy made his decision to part ways with longtime caddie J.P. Fitzgerald during The Open at Royal Birkdale, and said he did so because “in order to preserve a personal relationship, I had to sacrifice a professional one.”

McIlroy made official Wednesday what had been reported earlier in the week and was obvious when he showed up at Firestone Country Club for this week’s WGC-Bridgestone Invitational without Fitzgerald.

Harry Diamond, McIlroy’s childhood friend, will caddie for at least the next two events.

The player-caddie relationship with Fitzgerald dated to July 2008, when McIlroy was 19 and in the early stages of his pro career. Fitzgerald, who previously had caddied for Darren Clarke and Paul McGinley, had recently parted ways with Ernie Els.

Together, McIlroy and Fitzgerald won four major championships, with 13 victories on the PGA Tour and 13 on the European Tour (the majors and WGCs count for both). McIlroy also won last year’s FedEx Cup, which came with a $10 million bonus.

On the PGA Tour alone, McIlroy has earned more than $36 million in his career. Last year, McIlroy acknowledged he had given Fitzgerald a $1.05 million bonus from the FedEx Cup windfall. When McIlroy first disclosed the story, he said Fitzgerald had texted him to say: “A tsunami just hit my bank account, so thank you very much.”

Throughout their tenure, there had been signs of strain — even though McIlroy went so far as to praise Fitzgerald last month after the first round at The Open, where he had been 5 over par through six holes and rallied to shoot 71. He eventually tied for fourth.

“I was getting very hard on him on the golf course and I didn’t want to treat someone that I — I don’t want to treat anyone like that, but sometimes this game drives you to that,” McIlroy said Wednesday. “But I felt like it was the right thing to do and I don’t think there was any good time to do it.

“It was a really tough decision to make, but I thought, ‘I’m coming to Firestone, I have four tournament rounds to either get to know someone or get used to having someone else on my bag going into the last major of the year.’ And that’s really it.

“I thanked J.P. for everything. J.P. knows how much I think of him, how much he means to me, what we’ve achieved together. And it wasn’t an easy decision, but at the end of the day I felt like it was a change that I needed to make because … I got to the point where if I didn’t play a good shot or if I made a wrong decision, I was getting more frustrated at him than I was at myself.

“I would much rather be angry at myself for making a wrong decision than being angry at him, and that was really why.”

Diamond was McIlroy’s best man at his April wedding, and McIlroy said Diamond is a good player in his own right. He caddied for McIlroy as far back as 2005 and the two played competitive junior golf together. They grew up in the same suburb of Belfast — Holywood, Northern Ireland.

Whether Diamond goes beyond next week’s PGA Championship is unknown, McIlroy said.

“We’ll see how the next two weeks go, but I’m not ruling anything out,” McIlroy said. “It could be two weeks, it could go longer than that. Jeez, if we have a couple of good weeks here, you never know. We’ll see how it goes.

“But I think that decision will be up to Harry rather than me. Obviously he’s got his own thing going on back home, but a couple of wins might change things.”