Rory McIlroy\'s first round on European soil in seven months proved to be an explosive one and could yet land him in trouble with golf\'s authorities. In a fit of anger during his bogey-filled opening round of 2-over 74 at the PGA Championship on Thursday, the world\'s top-ranked player tossed his club to the ground in despair. The incident came after he sent his fourth shot on the par-5 12th into a greenside bunker, moments after his second had flown narrowly out of bounds. It was one of five bogeys the Northern Irishman made in his first round at Wentworth. He also hit a double bogey, and lies eight shots off the pace. \"It\'s pretty disappointing,\" said McIlroy, whose No. 1 ranking is under threat from Luke Donald this week. \"I feel like I\'m playing well, I just need to go out there and shoot a score.\" He could be fined as much as 10,000 pounds should his actions be deemed a minor breach of the European Tour\'s guidelines on course etiquette. \"I have not yet had the chance to view the incident but I will be requesting a tape and if any breach ... is found, then appropriate action will be taken in due course,\" tournament director David Garland said. McIlroy said his club-throwing outburst on the 12th, one of four par 5s on the course, was simply a release of frustration. \"You think about the par 5s and you should be taking advantage there,\" he said. \"Standing on the first tee, 3 or 4 under is the worst you should be shooting. In fact, the par 5s weren\'t the problem - he eagled No. 4 and birdied No. 17. It was his putting that let him down, especially around the turn where he dropped four shots in five holes, culminating in the error-ridden showing on No. 12. \"I struggled with the pace of the greens,\" said McIlroy, who has had to adjust to the slowness of the putting surfaces as he is based in the United States. His missed cut at The Players Championship two weeks ago was the first time he failed to make the weekend in 23 tournaments. His consistent run of form had helped him to top the rankings for the first time in March thanks to a win at the Honda Classic and then again in April. On both occasions, he replaced Donald. However, at the PGA Championship, he has only one top-10 finish in four previous tournaments.