England's Ross Fisher and Germany's Martin Kaymer played through heavy morning rains Thursday as they shared the early Irish Open lead with opening rounds of 3-under 69.
Tournament host Rory McIlroy, the world's No. 3-ranked player, was starting later in milder afternoon conditions at Ireland's K Club resort. Seeking his first victory of the season, the Northern Ireland native has rarely fared well at this tournament, missing the cut for the past three years.
Many early starters struggled amid chilly, blustery downpours, with only nine golfers in the 78-strong morning field finishing under par at the 7,350-yard (6,719-meter) Arnold Palmer-designed course.
The K Club in County Kildare west of Dublin is hosting a top tournament for the first time since Europe routed the United States in the 2006 Ryder Cup.