If Fenerbahçe were to win tonight, they needed to produce a much-improved performance from the one that saw them lose to bitter rivals Galatasaray at the weekend to get anything from the game.
However, that defeat appeared to be playing on Fener’s mind early on, as they struggled to contain their guests.
Inside the opening two minutes, Jaden Oosterwolde needed to produce a last-gasp interception and clearance to prevent Noah Sadiki from tapping into an empty net, while Franjo Ivanovic twice forced Dominik Livakovic into action.
Mourinho’s men improved as the half progressed though, and they ultimately landed the first blow of the encounter. Caglar Soyuncu was the unlikely goalscorer, scooping Rodrigo Becao’s knockdown over St. Gilloise goalkeeper Anthony Moris from close range.
The Belgian outfit pushed forward in response and continued to look dangerous, but clear-cut chances were non-existent prior to the halftime whistle.
Immediately after the restart, Sarı Kanaryalar went in search of a second that would have given them extra breathing space, with Youssef En-Nesyri the most likely scorer.
He first fired over the bar from a dangerous position inside the penalty area, before seeing a header cleared off the line by Charles Vanhoutte.
The visitors, meanwhile, saw a Christian Burgess header sail beyond the post, before efforts from Sadiki and Alessio Castro-Montes were easily held by Livakovic
En-Nesyri will have wondered how he hadn’t got himself on the scoresheet when he wasted another golden opportunity, this time heading straight when unmarked, but the Moroccan was soon involved in a key moment that went some way to deciding the outcome.
As the centre-forward bore down on goal, he was tripped on the edge of the box by last man Kevin Mac Allister, who was subsequently sent off for his troubles.
The free kick came to nothing, and Fenerbahce initially ran down the clock rather comfortably.
And they even had a second to celebrate – albeit in fortuitous circumstances, when Burgess bundled into his own net after Moris had denied Bright Osayi-Samuel.
The latter’s cameo was an eventful one, with him picking up a second yellow card for a late challenge on Ousseynou Niang in the box.
From the penalty spot, Ivanović was denied by Livakovic, but the rebound from his later strike that hammered the woodwork was stroked home by Ross Sykes.
But that proved to be too little, too late, as Fener held on to extend their unbeaten run against Belgian clubs to five matches. They travel to FC Twente next in this competition while St. Gilloise, without a win in five themselves, will hope to have ended that streak before they host Bodø/Glimt next week.
Flashscore Man of the Match: Caglar Soyuncu (Fenerbahce)