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Fernandes scored a first-half brace as United went in 3-0 up at the break, while the hosts had defender Dani Vivian sent off after giving away a penalty and having been deemed to make no attempt to play the ball.

After the result, Athletic's hopes of returning to its home stadium for the final are hanging by a thread.

"You can never predict a scoreline like that. Very tough team, the atmosphere was crazy. I knew they were very passionate, but never knew it was like this," Fernandes said after the match.

"The result for us was unbelievable. We should push a bit more in that second half, but we controlled the game and that is good.

"For us, it was brilliant to stay on the ball and they won't press as they preferred. If they press we could play through them. We were a little slow on the ball, but they wanted to keep the result like this to try come back in the next game."

His brace took the Portuguese to 34 goal involvements in all competitions this season – 18 goals and 16 assists.

It marks an impressive season for the Manchester United captain, who took until late October to net his first goal of the season in any competition.

"I knew I was around the thirties, but I didn't know how much exactly. It is a big part of my game and I need to take that responsibility. The club bought me because I scored 32 goals in a season," he said.

"Sporting is massive club, but United is a global club. Unbelievable the attention and pressure we get.

"I feel the pressure. That's the good thing about football and that's what we have to enjoy. When I finish my career that will go away and I will be much more relaxed.

"When I die I will have a lot of time to lay down with myself."