The Spaniard scored the third of United's goal from a fine set-up by Fred as Ole Gunnar Solskjaer's team all but wrapped up a place in the tournament's last eight, but it was the eerily silent stadium that was the game's main feature.
"I don’t remember playing behind-closed-doors," said Mata. "It was a different game, but I think we did really well. It wasn’t easy, because they are a team that press a lot, we didn’t have our best game in terms of passing, but at the end of the day we scored five goals.
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"It does feel strange. It is like training, when you do a game in training there is no crowd and it felt a little bit the same. We did what we were asked to do and we need to act accordingly and trust the experts."
United took the lead when Odion Ighalo fired a brilliant volley into the roof of the goal after 28 minutes, but it wasn't until the second half that they started to take control.
Daniel James made it two shortly before the hour, and once Mata had put the game beyond doubt Mason Greenwood and Andreas Pereira netted twice more in injury time to complete the rout.
"It was a fantastic ball from Fred, it was difficult to see my run because of players in front of him. It was a beautiful left-foot, vision and I could finish. Then in the last 15 minutes we killed the game."
Mata was keen to talk up the contribution of Bruno Fernandes, who continues to impress since making his January switch from Sporting Lisbon.
"I think we understand football the same way," said Mata. "We like to play the same way, and playing with each other. It is great to have him in the team and also Odion, scoring in almost ever game that he plays."
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