The Portuguese coach believes the tie remains in the balance after Danny Welbeck and Cristiano Ronaldo scored in an entertaining encounter at the Santiago Bernabeu
A Danny Welbeck header from a corner was cancelled out by an equally impressive headed finish from Cristiano Ronaldo in the first half, but neither side could find a further breakthrough on Wednesday evening.
And, despite United effectively holding a one-goal lead courtesy of the away goals rule, Mourinho confidently predicted his side can cancel that out at Old Trafford.
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"Fabio [Coentrao] had a really good chance when he hit the post, then the first time they go in our half they score a goal out of nothing.
"To be losing 1-0 is not a good situation. After halftime they tried but Man U played for the result.
"Their defence was deep but now it is our time to go to Old Trafford and I think 1-1 is not a bad result because everything is open and we can score more than one goal there."
The Portuguese insisted he expected an open game at the Santiago Bernabeu, but expressed surprise at the deep position taken up by United's defence.
He continued: "It was nothing new. It was not a surprise. It was basically what I was waiting for, which is everything open for the second leg and I was thinking this will go to the last minute.
"They changed the way they play. They played very deep in the second half. I don't think Rio or Evans put a foot in our half. I think they were waiting our set pieces so they could counterattack for the second goal, but we kept them out.
"Normally that would change the game, but they did well. The result is open if you ask me a percentage, I wouldn't change my thoughts. It is still 50/50."
The former Chelsea boss also hailed the defensive heroics performed by Sir Alex Ferguson's side as Los Blancos pushed for a winner.
He explained: "They [United] had to be champions in the second half and champions out of context because we were chasing the game and they were waiting for an opportunity, but this is the CL.