The late equalising goal for Anderlecht in the 1-1 home draw with United give them some hope, slight as it might be considering they have yet to register a win in 15 trips to England.
If this record was not dismal enough then factor in Utd have won all 5 European home games this campaign and won all their contests at Old Trafford against Belgium opposition then Anderlecht would be aware that history was stacked against them.
Yet at the end of the first 45 minutes it was the Belgians in the ascendancy. After a bright start they fell behind to an early Heinrich Mkhitaryan effort but rallied quickly and looked sharper and more confident on the ball than Utd who did not help their cause with carelessly giving away possession and looking shaky at the back.
With Mkhitaryan taking full advantage of a quick Utd break involving Paul Pogba and Marcus Rashford it seemed as if the home side would go on and build on this early advantage, but it never happened.
Twice in quick succession after taking the lead first Pogba brought a fine save from Martinez Rubin then Rashford saw his shot palmed behind. But with a second goal failing to materialise the visitor's took heart and began creating chances of their own as Utd's defence began to look vulnerable.
Again Utd failed to clear and Youri Tielmans shot from distance crashed against the cross bar and skipper Sofiane Hanni reacted quickest to to blast the equaliser and bring the tie level 2-2 on aggregate.
The Belgian's finished the half the stronger and Utd left the field to muted boos from the home support whilst the Anderlecht fans ended as they had begun in full voice.
Within a four minutes of the restart both teams could have scored. Lukasz Teodorczyk easily found space but his weak strike was easily stopped by keeper Sergio Romero. Utd hit back and Luke Shaw from a tight angle whipped his shot across the face of goal narrowly missing the far post.
But still it was Anderlecht who looked the sharper and more confident as Utd struggled to impose themselves. In a rare Utd threat Zlatan Ibrahimovic headed down to Rashford who, with a clear sight of goal, dragged his effort wide.
A long hopeful ball upfield allowed Rashford to out-muscle his marker and burst clear but he took the ball too far around the keeper and the danger was cleared. Suddenly Utd had come to life and when Ibrahimovic was unmarked close to goal the home fans could only groan as the Swede's weak effort was blocked a feat he repeated later with an embarrassingly wayward shot.
Now it was the home side showing some urgency and making all the running as Anderlecht defended ever deeper. Rashford found the side netting just before the end of ninety minutes and so the game went into extra time.
Utd continued to press and a spectacular goal bound overhead kick by Pogba was blocked by an Anderlecht defender just as the additional 30 minutes began. The home side did find the back of the net through Pogba but it was disallowed for substitute Marouane Fellaini fouling.
The final fifteen minutes began and almost immediately Utd scored when Rashford collected a knockdown inside the penalty area, turned and fired his team ahead on the night and 3-2 on aggregate.
A late Anderlecht rally caused a few flutters but Utd held on for an important win which keeps the Europa dreams alive
Full Time AET
Man Utd: 2 (Mkhitaryan 10, Rashford 107)
Anderlecht: 1 (Hanni 32)
Man Utd through to the semis 3-2 on aggregate