Holders Ajax enjoy Dutch Cup stroll
El Hamdaoui opened the scoring after 13 minutes from an assist by Florian Jozefzoon, who doubled the lead 10 minutes later.
Jan Vertonghen headed home a third on the stroke of half-time before El Hamdaoui and Urby Emanuelson struck after the break.
Danny Koevermans hit a double in PSV Eindhoven's 3-0 home win over second division Sparta Rotterdam.
Roda JC Kerkrade ousted last year's beaten finalists Feyenoord on penalties after a 1-1 draw after extra-time.
Roda keeper Przemyslaw Tyton had saved a penalty in extra time when he denied Leory Fer.