The Greenock golfer was four under par at the time and just three shots off the lead when he had to call a two-shot penalty on himself after playing the ball belonging to Dermot McElroy, his 21-year old Irish amateur partner.
Both players had split the Fota Island first fairway that they were playing as their 10th hole, with Doak walking up to his Titleist and putting his second shot on the green.
McElroy then followed the Scot on to the green where it soon became obvious they had played each other's ball. "It was a great round except for having to call a double bogey on myself after hitting a wrong ball," said Doak. "Both Dermot and I have two black dots on our ball. He marks his with a black dot on the numbers and I mark my ball with a dot above the number.
"The thing is that I have done it before as I then had three dots on my ball and the fellow I was playing with also had three dots. So it's just unbelievable I've let it happen a second time. After going out in four under, something like that just put me off my stride. I then bogeyed my 13th and birdied the next but dropped a shot at the last."
Despite the mishap, Doak's two-under-par 69 was the best opening round of the 14 Scots competing in Cork. It was also five shots better than Rory McIlroy, who suffered from a combination of missing clubs, lack of sleep and difficulty finding the fairways to languish 10 shots off the lead. McIlroy managed just three birdies but also posted twice as many bogeys in the superb scoring conditions.
Ilonen certainly took advantage, and birdied five of his closing seven holes on the occasion of his 300th Tour event. The 34-year old Finn, who has won three times on the European Tour, needed just 26 putts to snatch a two-shot lead from Sweden's Robert Karlsson and Gemany's Marcel Siem.
It is Ilonen's fifth course record as he sets about claiming Scandinavian domination of the Irish Open following Dane Soren Hansen's 2002 success the last time it was staged at Fota Island. However, Ilonen is not expecting his progress in Cork to be making too many waves back home.
"If I do well over the weekend, then it should make the media but with the World Cup going on right now, it will be 99%World Cup news in the media and one percent of something else," said Ilonen. "What I am doing will be the something else now. But then the good thing Finland is not playing in the World Cup."
McIlroy, the highest world-ranked player in the field, hit eight of the 14 fairways and then had 30 putts. It is the second year in succession the double major winner has started an Irish Open with a 74 and he now needs a six to eight-shot turnaround today to be assured of playing all four rounds.
While McIlroy finds himself languishing down the field, he assured the huge crowds who will flock to the course today of a better showing.
"I need a score that gets me back into the tournament and something like a four or five under par, and try to make as many birdies as I can," he said. "All the par 5s out here are reachable for me and there's a few par 4s I can also reach, so there's plenty of chances.
"But sometimes where you play a week like last week's US Open when you're not making many birdies, it's hard to get back into the mind-set where you are going to have to make a lot of birdies.
"So hopefully this round is the bad one out of the way and, besides, three over par here at Fota Island is a lot worse than three over par at Pinehurst."