The 33-year-old Finn secured his second career Stockholm title at No. 13, when closest pursuer Jonas Blixt faltered to a double-bogey while Ilonen chipped to five feet and then sank a birdie putt for a four-shot lead.
He finished at 21-under-par 267 at Bro Hof Slott Golf Club, claiming his third European Tour win overall.
Blixt ended three behind at minus-18 after a final-round 68.
Claiming sole possession of third place one shot further back was Bernd Wiesberger (6-under 66).
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