World number one Rory McIlroy faces a fine from the European Tour after throwing a club in frustration during the first round of his defence of the BMW PGA Championship title on Thursday.
McIlroy is looking to claim a third win in four events, having followed his victory in the WGC-Cadillac Match Play with a third consecutive top-10 finish in the Players Championship and a seven-shot triumph at Quail Hollow on Sunday.
However, the 26-year-old struggled to keep his emotions in check after carding four birdies and three bogeys in a round of 71, hurling his three-wood down the 17th fairway after hitting a poor approach to the par five.
McIlroy also threw his ball into the water on the 18th after missing a birdie attempt and conceded afterwards that mental fatigue was a factor in the fourth of five tournaments in succession.
"Physically I am all right - I got back to my hotel at 4:30pm (on Wednesday) and did not leave it until 6:30 this morning - but mentally I could feel myself getting a little angry out there," said McIlroy, who also threw his 3-iron into a lake at Doral during the WGC-Cadillac Championship in March.
"Acceptance of bad shots is the thing I have been doing so well and I feel like my patience was wearing a bit thin today. I just need to stay in control of my emotions because I feel like that's one of the things - if I'm a little tired or a little fatigued mentally, I'll start to be hard on myself and start to get down on myself.
"I played okay. There weren't really any aspects of my game I thought were really good, but at the same time I don't feel any aspect of my game was really off."
McIlroy was only three off the pace when he finished, but ended the day six off the lead held by former Ryder Cup team-mate Francesco Molinari, who posted a flawless 65.
Molinari, whose brother Edoardo retired with a wrist injury after playing 16 holes in eight over, was joint second in the Spanish Open last week and has an excellent record at Wentworth, having finished seventh, ninth and seventh the last three years.
"I think I missed one green on the third and chipped up to two feet, so it was as stress-free as it could be round here," said the 32-year-old, who has recorded just one top-10 finish in 10 starts on the PGA Tour this season.
"I love this place and it's good to be back. It rewards accuracy, which suits my game.
"Playing in America is a new challenge and I think it's helping my game to improve. Hopefully I will get my rewards soon."
A win on Sunday could lift Molinari from 66th in the world rankings to inside the top 30, securing his place in the US Open and Open Championship.
"I missed the Masters this year after 22 majors in a row and it was not a nice feeling, so I hope I will be back soon," he added.
Molinari enjoyed a two-shot lead over former European number one Robert Karlsson, with England's Chris Wood, Scotland's Marc Warren, former US PGA champion YE Yang and Spanish pair Miguel Angel Jimenez and Jorge Campillo all four under.
Peter Lawrie heads the Irish contingent at Wentworth on three under, while compatriot Damien McGrane is just one shot further back after a round of 70.
Three-time major winner Padraig Harrington lasted just two holes before retiring with a shoulder problem, but Scotland's Stephen Gallacher didn’t even get that far as he was forced to withdraw before play began due to a wrist injury.
There was better news for England's Andrew Johnston, who won a BMW M4 for a hole-in-one on the 10th, which he marked with an exuberant chest-bump celebration with a friend in the gallery.
