The 12-year-old amateur Ye Wocheng missed the cut at 14 over after a pair of 79s.
But China's Dou Zecheng became the youngest at 16 to make the tournament cut with a 70-72 for a 2-under total.
"I am happy with my scores, and feel excited to make the cut, so I will enjoy my game through the weekend," said Dou, who will try to qualify for the U.S. Open. "I am not thinking too much about my score, just try my best, and get some more experience."
Ilonen birdied four of his last five holes to finish at 12 under and move ahead of Australia's Brett Rumford and Thailand's Kiradech Aphibarnrat, who had 67s.
Ilonen matched the Binhai Lake course record set last year by Sweden's Alexander Noren. He also equaled his lowest round at the 2009 Madrid Masters.
Defending champion Branden Grace of South Africa birdied seven of his last 10 holes for a 67 and trails the leader by nine shots.