US President Donald Trump is set to jet in to attend the event over the weekend, which is being held at his resort in the County Clare village of Doonbeg.

Northern Irishman McIlroy is defending his title and aiming to win for the first time since collecting a second green jacket at the Masters in April.

A double bogey six at the 13th set the world number two back, but those were the only dropped shots of his round, which was disrupted by the blustery conditions leading to a glacial pace of play.

"I hung in there, shot under par, and at least don't feel like I'm out of the tournament. A good day tomorrow gets me right back in it," said the six-time major champion.

"There were a couple of things that were tough today. Obviously, the wind and the strength of the wind was one thing, and then the pace of play."

"This course isn't conducive to sort of letting you get in a flow. Especially the first two days with so many people in the field, there is a lot of stopping and starting."

Niemann made four birdies in a row from the 14th to forge ahead.

"It's a really tricky course and a really fun golf course to play with, especially with the Irish weather," said the Chilean. "(I'm) getting used to this weather and the rain, so it was fun."

Delays caused by the conditions meant that some players will have to return early on day two to complete their opening rounds.

Home favourite Shane Lowry is among a five-strong group, two shots behind Niemann after a 67.

Adrian Meronk, Maximilian Steinlechner and Renato Paratore were also at three under when bad light brought their opening day to an end without completing their rounds.

Jon Rahm was level par on a rare appearance back on the DP World Tour as speculation surrounds his future after LIV Golf filed for bankruptcy in the USA.