Manchester United were left kicking themselves after conceding a late goal in a 1-1 draw away to Anderlecht in the Europa League quarter-final in Brussels on Thursday evening.
Henrikh Mkhitaryan slotted home from an acute angle after Martinez Ruben saved well from Marcus Rashford.
The goal was the Armenian's ninth in 21 games for the Red Devils, and gave a relieved Mourinho a reason to celebrate after a solid defensive performance from the Belgian outfit in the first half.
Midfielder Leander Dendoncker levelled the tie in the 85th minute, rising highest to head home and give the Belgian side a boost ahead of the second leg.
Henrikh Mkhitaryan is the 1st Man Utd player to score in 4 successive away European apps since Ruud van Nistelrooy (5 between 2002-2003) pic.twitter.com/c5tE47okEs— Sky Sports Statto (@SkySportsStatto) 13 April 2017
Anderlecht started the game strongly, with the likes of Dennis Appiah and Massimo Bruno making life uncomfortable for the United defence. Bruno had a golden opportunity early on, but squandered it, kicking the air after a horrible miscue on the edge of the visitors box.
United struggled to get in to the game early on and almost went behind, with a Frank Acheampong cross fizzing agonisingly across the box and evading everyone.
But t he Reds started to grow in to the game after a sluggish start, with Rashford beginning to find pockets of space of the left side of the Anderlecht defence.
The Englishman threatened to put the away side ahead in the 19th minute with a dipping shot from 18 yards, but his shot was slightly overhit, the ball sailing just over the left hand side of the goal.
Manchester United were finally rewarded for a spell of dominance in the 36th minute. Rashford's snapshot from just inside the box was palmed away by Ruben and straight in to the path of Mkhitaryan, who reacted quickest to sweep the ball home at the back post.
It was a crucial away goal for the English side, who had struggled to pick holes in a solid Anderlecht defence until this point.
The Belgian side were not to be deterred after falling behind, and they came out fighting in the second half. United partly had Antonio Valencia to thank for their clean sheet remaining intact; the wing-back hooking away Bruno's shot before bravely blocking a powerful follow up from Acheampong.
United looked to take control of the game after the break, with Anderlecht having to chase the tie before their visit to Old Trafford in the return leg. Marouane Fellaini replaced Marcus Rashford to try and shore up the United defence, with the ex-Standard Liege receiving a frosty reception from the home crowd.
But Fellaini could do nothing to prevent Anderlecht pulling level with five minutes to go. A cross from the left was met by Leander Dendoncker, whose powerful header beat Sergio Romero in the United net and gave the home side a glimmer of hope.
The goal was the Belgian sides first shot on target, such was United's dominance on the night.
United were unable to create any clear cut chances as the game drew to a close, with Fosu-Mensah lucky to escape with just a booking in the dying seconds after a lunging two-footed tackle on the edge of the Anderlecht box.
Although United will still be considered favourites to progress, the home side can take heart from the fact that they have a foundation to build upon when they make the trip to Manchester on Thursday 20th April.