Darren Clarke conceded there were nerves and he was emotional as he struck the opening tee shot of the 148th Open Championship at Royal Portrush, where Webb Simpson was leading after a fine birdie streak.

Local hero Clarke was given the honour of starting Thursday's play and made a flying start by going three under par through his first five holes on the Dunluce links.

It was momentum the 2011 Open winner could not maintain, though, and the 50-year-old eventually signed for a level-par 71.

Reflecting on his opening tee shot, Clarke said: "On the first tee this morning a little bit [I felt the nerves], and then on the last. 

"There's always nerves. If any professional golfer tells you they haven't got nerves when you start a tournament, you're in the wrong job.

"It was more emotional than I thought it was going to be, to be honest. I knew the golf course was going to be fabulous."

The heavy downpours on the final practice day on Wednesday had been replaced by calmer conditions on Thursday morning and Clarke expects plenty of low scores throughout the week. 

"I think you guys know better than me, after having spoken to all the players and stuff, they're really enjoying the golf course," Clarke added. 

"It is a proper, fair test of golf. The scores are going to show that, not just today but at the end of the week. It was one of those things that I was very proud to be standing on that first tee hitting the first shot."

American Simpson was one clear at the top of the leaderboard having reached five under walking off the 15th tee, a run of five gains between the seventh and 13th propelling him up the field.

Irishman Shane Lowry and Scotland's Robert MacIntyre were each one shot back, while Sergio Garcia, Alex Noren and Dylan Frittelli - the last man in the field to qualify for The Open after winning the John Deere Classic on Sunday - were at three under par.

Rory McIlroy was making some progress from his dreadful start, which saw him make a quadruple-bogey eight at the first and drop another stroke at the fifth, as a gain at the seventh meant he was at four over.