Ferrero, seeded No. 24, was leading 1-6, 6-4, 7-6 (7-5), 1-0 when Simon, the ninth seed, retired.
The Spaniard is in the fourth round at the open for the first time since 2003.
The No. 2 and 3 seeds, Andy Murray and Rafael Nadal, played later matches.
Copyright 2009 by United Press International.