Rory McIlroy opened the defense of his BMW PGA Championship title on Thursday with a 1-under 71 that left him four strokes behind clubhouse leader Robert Karlsson.

McIlroy says "I felt like I left a couple of shots out there" and that "I did not do anything that good and there is definitely room for improvement over the next few days."

Karlsson made six birdies for a round of 67. The Swede birdied two of the final three holes to take the overall lead.

Miguel Angel Jimenez, Jorge Campillo and Chris Wood were a shot back on 4-under.