There are over 150 players in the field.
The second major championship of the year - the US PGA - begins at lunchtime at Oak Hill in New York.
There are four Irish players in the field of 156 - Rory McIlroy, Shane Lowry, Seamus Power and Padraig Harrington.
McIlroy's last major win was in the PGA back in 2014, he's out just after 1pm Irish time.
He will be followed among the early starters by Shane Lowry and Padraig Harrington, with Seamus Power beginning his challenge later on.
The County Down star has spoken about his gameplan as his bids to put his Masters disappointment behind him.
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