Defending champion Ross Fisher was one of five players in a share of the clubhouse lead at the Irish Open presented by Discover Ireland.
A four under par opening 67 at Killarney Golf & Fishing Club saw The Ryder Cup star join Australian Richard Green, Swede Niklas Lemke, Dane Sren Hansen and home favourite Colm Moriarty.
Meanwhile Rory McIlroy pulled off what he called "one of the best shots I've ever hit", but was left wishing he had produced another on the last hole.
Playing his first tournament on home soil since his runaway US Open Championship victory in June, the 22 year old saved par on the 14th after a spectacular hook round the trees from deep rough.
But, three under par and only one off the lead with one to play, McIlroy went from a fairway bunker into water and double-bogeyed.
Lemke, in the event because of his third-placed finish in the Nordea Masters on Sunday, went to five under on the 17th but he bogeyed the last.
With new Open Champion Darren Clarke and three-time Major winner Padraig Harrington among the later starters - Clarke bogeyed the first hole - and last year's US Open Champion Graeme McDowell managing only a 72, McIlroy had the chance to set a really challenging total.
"At four under through ten things were going along quite nicely," he said, "but I didn't drive it great all day and I played some scrappy golf coming in."
The approach to the 14th was a notable exception to that - "all I was trying to do was get it in the front bunker" he commented on a 130 yard shot to within 20 feet of the flag that he had to move nearly 50 yards right to left.
"My driving caught up with me at the end. I just need to be more decisive on the tees - I was stuck in two minds."
McDowell commented: "It was a funny day. I didn't hit it in the fairway much and didn't make much on the greens and then after birdies at 14 and 15 steadied the ship I was a yard in the gorse on the (par five) next and made bogey.
"It was nothing disastrous I suppose and I'm not out of it by any means."
Clarke remained one over after six, while Harrington bogeyed the short third, but birdied the next to be four behind the six joint leaders - Fisher, Green, Moriarty, Lemke, Hansen and German Marcel Siem, who turned in a best-of-the-day 31.
Irish amateur Paul Cutler was only one worse than that, his round having started with an eagle two after he pitched in from 133 yards.
By coming home in a spectacular six under 30 - he birdied six of the next seven holes after the turn - Swede Christian Nilsson was the new clubhouse leader with a five under par 66.
Clarke and Harrington both stood one under with eight to play.
