Ilonen will seek his third career European Tour win, and first since 2007, after finishing the day at 18-under-par 198, two better than Alexander Noren.
Noren outdid Ilonen Saturday with a third-round score of 8-under 64, moving into sole possession of second at Bro Hof Slott Golf Club.
First- and second-round co-leader Matteo Manassero stumbled down the stretch Saturday, carding a double-bogey on the final hole to end with a 1-under 71.
That put him into a third-place tie with Jonas Blixt (66) at 14-under.
Rikard Karlberg was in fifth place at 12-under.