Teenage substitute Amad Diallo opened his Manchester United account in style but Simon Kjaer's stoppage-time header denied Ole Gunnar Solskjaer's men victory against AC Milan in the Europa League. The eagerly-anticipated last-16 clash between these European heavyweights produced drama on Thursday night and set-up an interesting return fixture at San Siro next week. Half-time substitute Diallo's superb, improvised header looked to have secured a hard-fought first-leg win at Old Trafford, only for Kjaer's last-gasp header to seal Milan a deserved 1-1 draw. In truth, Solskjaer's side would have been fortunate to be going to Italy in the lead given how the absentee-hit Rossoneri outplayed the hosts for large periods. United looked a shell of the side that impressively won at Manchester City on Sunday Manchester United manager Ole Gunnar Solskjaer said: "That equaliser makes it harder but it was always going to be down to the second game. We were too slow with the possession, it is sometimes hard off the back of a game like Manchester City." Milan manager Stefano Pioli was proud of his team's "amazing" spirit at Old Trafford. "We are working to grow and bring Milan back where we belong," said the Rossoneri boss, who was annoyed to see Franck Kessie's early opener ruled out for handball. "These are the best games in that sense, so I was happy to face a team like United. "It was a great performance and a great result, but we need another perfect performance to qualify against such a strong team."