Marouane Fellaini powered home a header to open the scoring before Jesse Lingard doubled the lead just after half time. Rudy Gestede pulled one back for the home side before Antonio Valencia capitalised on a Victor Valdes slip to tap home into an empty net and seal the win.
And without the star qualities of Zlatan Ibrahimovic (suspended), Paul Pogba and Henrikh Mkhitaryan (both injured), Mourinho commended his side for earning three points on Sunday afternoon.
‘The attitude, the desire and our way of thinking. We don’t have A, B, C, D, E, F and G but we have L, M, N, S, O, P,’ the United boss said.
‘These guys gave absolutely everything. I think we started the game very well. Valdes made three fantastic saves before our first goal and we controlled everything until our second goal. And then they changed the play with Gestede and Negredo, they started putting long balls in the box.
‘We decided to defend with an extra defender but I think with the mistake of letting them push too much inside our box and it was a fighting 15 minutes.
‘They didn’t have chances but they had the ball in dangerous areas so the game was alive until the last second.’
Monday night’s clash with Chelsea, coupled with Thursday’s win over Rostov, meant three games in six days for United which took its toll on the fatigued squad as they made the trip to the Riverside Stadium.
United negotiated a difficult week and Mourinho had been vocal about his feelings on their packed fixture list. The win over Rostov in midweek meant United progressed to the quarter-finals of the Europa League.
And though their impressive run in the league has been blighted by 10 draws, the joint-most in the league, the important win over Middlesbrough closes the gap on the top four and leaves Mourinho’s men fighting for Champions League qualification on two fronts.
‘It is fantastic because we manage in the same week to go to the quarter-final of the Europa League, which is an important target for us,’ Mourinho added.
‘We got these three points which keep us in the race for the top four so we still have two doors open to play Champions League football next season so that’s the good thing.
‘But obviously it was too much for us: Rostov away, Chelsea with 10-men, Rostov again and now Middlesbrough. Injured player, tired players, suspended players. These guys today were magnificent.’