Ayew brothers bag Marseille last eight berth
Marseille, with a mostly reserve team, snatched the win against the run of play two minutes before half-time when Jordan powered down the right flank and his cross found elder brother Andre, who headed home from close range.
The brothers, sons of former Marseille player and Ghana international Abedi Pele, almost managed a repeat of the goal in the second half but Andre's header went just over the bar.
Guingamp, who won the French Cup in 2009, had numerous chances in the first half but their strikers failed to convert them.
Marseille defender Stephane Mbia and midfielder Edouard Cisse suffered leg injuries and were replaced in the second half.