Ruben Amorim’s side started on the back foot amidst a hostile atmosphere in Bucharest, where FCSB had lost just three of their previous 22 home group stage/league phase matches in the UEL.
The hosts had an early sighter after Mihai Popescu got on the end of a set-piece, but the Romanian’s volley drifted inches wide. From that moment on however, the Red Devils grew into the contest and stamped their authority on proceedings, with Kobbie Mainoo having two chances to open the scoring.
First, the 19-year-old midfielder brilliantly controlled the ball in the box but his weak volley was comfortably saved, before he skied an effort over the bar when picked out unmarked in the danger area by Rasmus Højlund.
United failed to capitalise on their dominance, with a lack of ruthlessness their only downfall. FCSB, on the other hand, struggled to build on their early momentum to leave the contest level at the break.
Amorim made an attacking double change ahead of the restart, and one of those introduced, Alejandro Garnacho, almost had an immediate impact after he pounced on a defensive lapse of concentration, bore down on goal and fired an effort against the post.
The visitors continued to dominate from there, with Højlund next to test Ștefan Tarnovanu after receiving the ball from Lisandro Martínez, but the Dane’s effort was scooped up by the Romanian stopper.
United didn’t let up however, and the breakthrough finally arrived on the hour mark when a well-worked move from a throw-in saw Kobbie Mainoo slide the ball across the face of goal, where Diogo Dalot arrived to fire home at the back post.
That moment proved pivotal as United doubled their lead less than 10 minutes later, with Mainoo on the scoresheet himself this time, sliding home from Garnacho’s cutback after winning the ball deep into FCSB territory.
Two goals after the hour mark proved to be the blows that the Romanian side were not able to recover from, as Elias Charalambous’ side failed to respond to the United double.
Amorim took the opportunity to make a host of changes with the result seemingly wrapped up, which puts the Red Devils into the draw for the last 16 as the only side to go through the league phase unbeaten, while the Romanians will have to settle for a spot in the play-offs.