Ilonen carded a final round of 70 at Fota Island to finish 13 under par, one shot ahead of Italy’s Edoardo Molinari, with Sweden’s Kristoffer Broberg and English duo Danny Willett and Matthew Baldwin another shot back in third. Sheffielder Willett’s reward is a place at The Open next month.
Graeme McDowell had been hoping to claim a first professional victory in Ireland in front of the massive crowds in Cork, but struggled on the greens and had to settle for a closing 71 and share of sixth with Magnus A Carlsson, his first top-10 finish in 13 appearances in the event.
Ilonen led from the moment he established a new course record of 64 at lunchtime on Thursday and although the record itself only lasted until Willett, aided by a hole-in-one, shot 63 on Saturday, the Finn took a one-shot lead into the final round.
Birdies on the second and fourth took him three clear of the field until Willett carded his second birdie of the day on the ninth, but that was as close as anyone got until Ilonen dropped his only shot of the day on the last, ironically after hitting an iron off the tee for safety.
“It was very much a Martin Kaymer-inspired win,” the 34-year-old said. “I sent a message to him last week that I really enjoyed watching the US Open. I very rarely enjoy watching it, I would rather play, but Martin’s win inspired me.
“I was thinking about winning this tournament from midday Thursday basically. Somehow the course looked easy to me and I felt we were going to see some crazy scores.
“I had a low one on Thursday to start with, and it was something that I was expecting, but I could see from the faces and comments of other players that they weren’t expecting it. I had a number in my head all week that I tried to get to and I missed it by a mile.”
Sheffield teenager Matt Fitzpatrick, the only amateur to make the cut in the US Open last week, finished in a tie for 29th in his first tournament as a professional following a closing 68.