Norrman, who improved 20 spots over the final 18 holes on Sunday, shot a bogey-free round to finish on 14-under 274 for the prestigious DP World Tour event in County Kildare.

His pursuers included third-round leader Hurly Long of Germany, whose even-par round of 72 had him finish at 13-under, and favourite McIlroy, who carded a surprisingly poor 74 to tumble 13 places down the leaderboard to finish in a tie for 16th.

West Australian Lee had briefly looked in shape to challenge for the title as he moved to just one shot behind the leaders after a blistering start but he slipped back after the turn to sign for a 70 and finish tied for seventh at 11-under, three shots adrift.

Norrman carded his only unblemished round of the tournament, following rounds of 68, 71 and 70 with seven birdies on Sunday.

“The front nine was huge. I was playing so-so and then I birdied the 7th and 9th to get some momentum going into the back. I think that was key today.” – Vincent Norrman.

"It means everything," Norrman said of his second DP World Tour title in his 14th appearance.

"Obviously, such a cool event to play. The fans have been incredible. I've really had a fun week."

“The front nine was huge. I was playing so-so and then I birdied the 7th and 9th to get some momentum going into the back. I think that was key today” Norrman, added.

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"It's a world-class event, and honestly I can't believe it's happened."

Four players tied for third at 12-under – Scotland's Grant Forrest (70), New Zealander Ryan Fox (70), South African Thriston Lawrence (66) and Ireland's 2009 champion Shane Lowry (68).