Mark Foster was the early clubhouse leader as the Irish Open finally returned to Northern Ireland after a gap of 59 years today but only because Padraig Harrington fluffed his lines.
arrington missed out on the chance of a share of the lead at Portrush after three-putting the ninth green.
Watched by a sell-out crowd - a first for the European Tour in a regular event - that included First Minister Peter Robinson and Deputy Martin McGuinness, Foster posted a six-under-par 66.
It put the Worksop golfer, winner of only one title in more than 300 starts, a stroke ahead of a group which included Harrington and defending champion Simon Dyson.
Out on the world famous links, however, Indian Jeev Milkha Singh went to the turn in a six-under 30 and with another birdie at the long 10th led the tournament by one.
Graeme McDowell, first of the three Northern Irish stars into action in a week which means so much to them all, had to be content with a one-under 71, double-bogeying the 581-yard pitch after seeing his pitch from the rough fly over the green into bushes.
Fellow major winners Rory McIlroy and Darren Clarke were among the later starters facing windier conditions, but not the heavy rain that greeted the first half of the field.
"When we came to the course the rain was sideways and yet people were queuing to get in," said Foster.
"It's amazing here and I've never heard a buzz about the course that there is in the players' lounge this week.
"It was throwing it down when we got up, but that was no surprise and you've just got to be professional about it.
"At least it was not that windy. But that will come - the course will show its teeth no problem."
He was six under through 10 holes himself, rolled in a nine-footer on the 13th, but bogeyed the 15th after chipping into a bunker and then hitting the flagstick with his recovery.
Harrington pitched in on the eighth - his 17th - for one of six birdies, but three-putting the last for only a par "knocked the shine off" the previous hole.
"It was incredible to see so many people here so early on a miserable day - very impressive," Harrington said. "And it's only Thursday!"
McDowell commented: "I was a couple under when the rain was at its worst, but then went in the bushes and was fighting from then on."
Singh remained seven under with six to play, while Foster was joined on six under when Swede Michael Jonzon birdied the second and fifth.
Scot Paul Lawrie, third in the Ryder Cup table, and European captain Jose Maria Olazabal were paired for the third tournament in under two months and both had three-under 69s.