The Northern Irishman finished tied for 22nd at five under in the FedEx Cup opener, which was claimed by American Hunter Mahan.
McIlroy feels his performance was better than his scores of 74, 65, 70 and 70 suggested at the Ridgewood Country Club.
"I'm coming away from this tournament a little frustrated. I feel I've played played better than what the score and the result suggested," he said.
"I struggled on the greens this week compared to the previous weeks. That was the big difference.
"I was converting those 10-15 feet birdie opportunities the last few weeks and I just didn't do that this week. That's the reason I wasn't able to make as many birdies."
Making those putts had helped McIlroy claim three straight wins – The Open Championship, the WGC-Bridgestone Invitational and US PGA Championship.
McIlroy said his run of wins was always going to come to an end eventually.
"It was going to come to an end sooner or later. The great thing about golf is that there's always next week," he said.
"I'm looking forward to going to Boston [for the Deutsche Bank Championship], where I've had success before. I've played well there.
"I feel like my game is in good shape so there's no reason why I can't go there next week and challenge for the title there."