The forward scored two quickfire goals before the break to hand Ivan Leko’s men a 2-0 lead.
The Mali international got the curtain raiser when he headed home a cross off Ruud Vormer and soon added the second after benefitting from goalkeeper Frank Boeckx’s error who goofed in his attempt to clear the ball and the attacker calmly slotted in.
In the 57th minute, Vormer scored from the penalty spot to increase the lead after Diaby was brought down in the box.
Jelle Vossen then added his name to the scoresheet to make it 4-0 with another penalty and, with three minutes left to play, Hans Vanaken sealed the victory off a Vossen cross.
The victory ensured that the Blue-Black continue their stay at the summit of the log with 47 points from 19 games, nine points clear of their closest rivals Sporting Charleroi and 13 points above Anderlecht who occupy the third spot.
Diaby has now scored six goals in his 21 appearances for the Blue-Black this season and will be looking to continue with this impressive form when they travel to AFAS-Stadion Achter de Kazerne to confront Mechelen on Wednesday.