Rory McIlroy played HUNGOVER at Canadian Open after celebrating his caddie's birthday - two weeks after filing for divorce from Erica Stoll

Rory McIlroy has incredibly revealed he was hungover during his first round at the RBC Canadian Open - because he was celebrating his caddie's birthday the night before.

McIlroy started slowly and didn't make a birdie on the front nine but found an extra gear after the turn and carded an impressive four-under 66 to finish the day tied third.

He told reporters after the round that he felt 'groggy' after celebrating Harry Diamond's birthday - Diamond is a childhood friend of McIlroy's.

It's the first tournament McIlroy has appeared at since the PGA Championship where, days before the start, it emerged he had filed for divorce from Erica Stoll after seven years of marriage. Diamond was McIlroy's best man for the wedding.

Ironically, McIlroy drove a wayward tee shot into a hospitality tent on the 17th hole.

'I obviously hit it into the hospitality and some guy yelled out "You need a wrist band to get in here!" - so that was pretty funny,' McIlroy said.

Incredibly, the Northern Irishman said that was the first time he had seen the back nine of the course.

'I played the back nine blind. Hadn't seen the back nine. Only played the front nine in the pro-am. I was sort of happy enough to get out of there in even par and not make a bogey.

'But once I got that nine holes out of the way I knew there were some chances on that front side and played probably much better on that front side. Four birdies there, no bogeys, was a good day's work.'

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