Manchester United struggled to put away a doughty FC Copenhagen before doing so in extra time, Bruno Fernandes again the hero for Ole Gunnar Solskjær’s side. The manager introduced Juan Mata for Mason Greenwood ahead of the extra half-hour and this proved prescient. On 95 minutes Anthony Martial was slipped in by Mata and while the superb Karl-Johan Johnsson saved from the Frenchman, a moment later Andreas Bjelland pulled him down. Clément Turpin, the referee, awarded United’s 22nd penalty of the season and Fernandes beat Johnsson to set up the club’s 17th European semi-final - against either Wolves or Sevilla, who play on Tuesday. Solskjær selected Eric Bailly to partner Harry Maguire with the recently injured Victor Lindelöf on the bench, while preferring Fred instead of Nemanja Matic in midfield. In sweltering heat United claimed a first corner though Fernandes’s delivery was defended easily. More pleasing was the rhythm Fernandes and Paul Pogba were establishing in midfield, pulling their white-shirted opponents around: precisely what was required in the sweltering conditions. A move that went Martial-Marcus Rashford-Martial-Mason Greenwood had Copenhagen turned, then relieved, when Johnsson could collect. Yet in moments play had moved to the other end as Copenhagen embarked upon a sustained period of pressure. Brandon Williams was beaten by Pep Biel who crossed from the right and United were thankful Bailly made the block. Then, Williams redeemed himself with a flying header beneath his bar after Martial inadvertently flicked on a Rasmus Falk corner. Next a hapless Fred passed straight to Jonas Wind and Copenhagen were in, the ball going to Mohamed Daramy. Bailly looked to have policed him before the forward swivelled and left the defender on the turf. A Maguire leg stopped the shot, the ball rebounded to Wind before Pogba cleared. This had Solskjær screaming at Fred for his lack of concentration, and United requiring a serious upturn in tempo. Confusion reigned when Turpin awarded them a penalty for what appeared a foul on Martial before VAR ruled offside. Better from United followed the drinks break. Fernandes fired a free-kick just over, Fred floated a 40-yard ball onto Greenwood’s chest, and a sequence involving Aaron Wan-Bissaka, Pogba and Rashford came close to having Martial clear in. United continued to buzz around. A Greenwood shot claimed a corner, while Fred pinged in another searching ball that had an unattended Rashford unable to collect close to the spot. Bailly was proving United’s most important defender. When Guillermo Varela wheeled past Williams the cross would have reached Daramy if not for another vital intervention from the Ivorian. As the break neared Greenwood fired home expertly but VAR ruled - correctly - that he was offside. This, though, did reflect how United had found a higher gear. This had to continue in the second half if a semi-final berth was to be secured. Copenhagen had different ideas. This was signalled by a high press that disrupted United and led to a free-kick for the Danes. Still, the red shirts flooded forward once more as slick Rashford footwork plus a Fernandes pass set up Pogba: his curled effort was wild. Greenwood apart this summed up the lack of composure in front of goal. It meant the manager might soon have to consider soon making a replacement (or two) unless United could make a breakthrough. When Martial, Fernandes, and Williams combined the final effort was scuffed by Fred: yet more franticness when a cool head was needed. Further frustration occurred when Greenwood’s left foot strike smacked against the right post and Rashford turned home: like the former earlier, the latter was offside. This was United at their most threatening. Greenwood was finding joy in more central areas as when a Fernandes lob had him just fail to bring the ball down in the area. Copenhagen were starting to feel the conditions more. The way Fernandes was allowed a touch before crashing a 25-yard diagonal off a post – the left this time – spoke of a wilting Danish rearguard. Yet as the final minutes approached Wan-Bissaka was fortunate Bryan Oviedo’s close-range shot hit his body and not an arm as a penalty might have been awarded. Solskjaer – finally – made a double change, replacing Bailly and Fred with Lindelöf and Matic. United had a scare when Varela went down in the area but no penalty ensued. Then, Martial’s late effort was superbly saved by Johnsson. By final whistle the deadlock remained and it now became a test of attrition and of managerial shrewdness: here Solskjær’s turn to Mata turned the tie for his team.