Ilonen surged up the leaderboard on a blustery third day at Suzhou Jinji Lake Golf Club with three birdies over the Finn's first four holes before edging ahead at 12 under par with a deft chip and run from the edge of the green at the par five ninth.
US PGA Championship winner Yang, who finished eighth at the Masters Tournament last week, managed just a solitary gain over his opening nine holes after making a successful up and down from a bunker at the par five second.
Donaldson had briefly held the lead after back-to-back birdies before a solitary bogey at the eighth dropped the Welshman, who finished sixth at the Open de Andalucia in Malaga at the end of March, back alongside Yang and Kim, who failed to improve from his overnight mark which had been enough for a one shot lead after two rounds.
The 21 year old Kim is in good form after following up a third placed finish at the Luxehills Chengdu Open at the start of April with a maiden victory on the Korean Tour at the SBS Tomato Open just last week.
Former champion Stephen Dodd, meanwhile, posted the third round clubhouse lead with a bogey free six under par 66 lifting the 2005 champion to ten under overall alongside Asian Number One Thongchai Jaidee and Spain's Pablo Larrazabal.
Trophee Hassan II winner Rhys Davies earlier produced a "special back nine" which included two eagles in three holes for a bogey free seven under 65 to improve to eight under overall.
Challenge Tour graduate Davies started brightly with a first hole birdie but that accounted for the only gain over the wetlands set up of the front nine.
But after holing a 70 yard pitch at the 12th for an eagle three at the start of the links style back nine, Davies holed a mammoth putt from the front edge two holes later before finishing with back-to- back birdies.
"It was very flat on the front nine. I got a birdie at the first and thought that might springboard something, but it just didn't quite happen," said the 24 year old, who opened with rounds of 73 and 70.
"And then it all started when I holed a 70 yard pitch on the 12th for an eagle. I had actually been threatening with a few wedge shots all week so you could say it was due, but it is always nice.
"I made a good up and down on the 13th and then got it on the front edge at the par five 14th in two and holed it from 50-60 feet.
"And I hit three irons into last two holes and holed it from 25 feet at 17 and then hit it to eight feet at the last.
"I have kept telling myself to be patient all week. I didn't play that badly over the first two rounds, but it wasn't quite happening. It wasn't quite happening on the front nine today but it certainly did on the back nine."