Killarney - David Howell opened up a one-shot lead after the first round of the Irish Open on Thursday, keeping at bay a pack of heavyweights including Major winners Padraig Harrington and Graeme McDowell.

Former Ryder Cup player Howell carded a seven-under-par 64, a round which belied his humble world ranking of 479.

"I've never wanted to give up, but it's crossed my mind that if I carry on playing as I did last year, I wouldn't have a career to be worried about," said the 35-year-old Englishman.

Five birdies and an eagle lifted Howell into a one-stroke lead over Ireland's Damien McGrane and Australia's Richard Green.

Green, who went out in 33 and came back in 32 like McGrane, said: "I felt very comfortable when I first saw the course on Tuesday and practised and played very nicely.

"I thought this is a nice old golf course for a change that's a little bit old school. I felt very comfortable out there. I played very nicely today."

McGrane outscored compatriot Harrington and McDowell by three and five shots respectively, while Darren Clarke and Michael Hoey shot 66, and Rory McIlroy 67.

McIlroy, at eighth in the world the highest-ranked player on view, made eight birdies, but also threw in four bogeys.

Harrington did not drop a shot, but admitted his keenness to end almost two years without a win is making him tense.

"Sometimes you find it very hard to win and then all of a sudden the floodgates open," he said.

McDowell, the US Open champion, said: "I just need to sharpen up across the board. I said someone would go super low, but you can defend this course by hiding the pins."

England's Robert Rock hit four birdies in the last six holes to hit a six-under-par 65, but he was then disqualified for signing for a wrong score.

Rock, seventh in the British Open two weeks ago, did not spot that his card had him down for a par on the 14th and birdie at the next instead of the other way around.

He said: "It's my fault. I checked it, but didn't see it and it's my job to do that.

"I don't think I've been disqualified for anything before. I'd have preferred it to be after an 80."

Leading and selected first round scores at the Irish Open on Thursday at the Killarney Golf and Fishing Club, Killarney (par 71; GBR and IRL unless stated):

64 - David Howell

65 - Damien McGrane, Richard Green (AUS)

66 Jean-Baptiste Gonnet (FRA), Noh Seung-yul (KOR), Anton Haig (RSA), Marcel Siem (GER), Darren Clarke, Brett Rumford (AUS), Paul Lawrie, Gonzalo Fdez-Castano (ESP), Michael Hoey

67 - Martin Wiegele (AUT), Francesco Molinari (ITA), Anders Hansen (DEN), Francois Delamontagne (FRA), Andrew Dodt (AUS), Johan Edfors (SWE), Danny Lee (NZL), David Drysdale, Rory McIlroy, Eirik Tage Johansen (NOR), Mark F Haastrup (DEN)

68 - Patrik Sjoland (SWE), Nicolas Colsaerts (BEL), Paul McGinley, Padraig Harrington, Paul Broadhurst, Simon Khan

69 - Barrie Trainor, Richard Bland, John Parry, Christian Nilsson (SWE), Ross Fisher, Robert Coles, Anthony Kang (USA), Sam Hutsby, Marc Warren, Alejandro Canizares (ESP), Markus Brier (AUT), Ariel Canete (ARG), Mark Foster

70 - Jeppe Huldahl (DEN), Graeme McDowell, Peter Whiteford, Sion E Bebb, Phillip Price, Matteo Manassero (ITA), Maarten Lafeber (NED), Simon Dyson, George Coetzee (RSA), Graeme Storm, Stephen Gallacher, Richard Finch, Fabrizio Zanotti (PAR), Bradley Dredge

Selected:

71 - Thomas Aiken (RSA), Marcus Fraser (AUS), Hennie Otto (RSA), Rick Kulacz (AUS)

72 - Scott Strange (AUS), Mark Brown (NZL), James Kamte (RSA)

74 - Justin Rose

75 - Peter Martin (AUS), Shiv Shankar Prasad Chowrasia (IND)

76 - Chapchai Nirat (THA)

77 - John Kelly (USA)

DSQ: Robert Rock (ENG)