After the match, Mata said he was still "up for" VAR being used in English football despite seeing his goal ruled out, while United manager Jose Mourinho suggested the offside call was too tight to use the technology.
"As I said in a few interviews after the game, even if this time it didn't play in our favour, I think in the future the VAR will be helpful for the referees, who always have a hard job".
Contain and crush; that is what Mourinho's team did on Saturday evening despite the absence of Paul Pogba, the £89 million midfielder, through illness. "I think our game is so lovely that to change we have to change for the better", said Mourinho, who had previously backed the use of VAR.
Lukaku's second goal, in the 55 minute, was similar but, if anything, even more impressive as the Belgian picked up the ball deep in his own half and set off upfield, outpacing his markers.
"I think our game is so handsome that to change we have to change for better", said Mourinho, whose side won 2-0 despite the disallowed goal.
"What I've seen is that there is a natural relationship developing between Alexis Sanchez and Romelu Lukaku", he added. And we have a strong team, strong bonding, strong team mentality. I felt I needed to make a little bit of a statement about the events. "If they find a way in the VAR that the VAR is always right and always brings the truth, I'm happy with that".More news: Russian Federation urges United States of America not to play with fire in Syria
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"Wesley Hoedt took advantage of some slack West Brom marking to head home his first goal for Southampton just 11 minutes in".
"Good counter-attacks, twice attacking the space well".
Brighton cruised into the last eight as fourth-tier Coventry City's fairytale run came to a crashing end in a 3-1 defeat.
Sheffield Wednesday and Swansea must try again after their tie ended goalless at Hillsborough in the early kick-off.
"It's one of the most hard games of the season and a good opportunity to bring joy to our fans, although, right now, we are absolutely focused on the Champions League against Sevilla". Pep Guardiola's side have blown away any suggestion injuries and fatigue could derail their quest to win the Premier League, Champions League, League and FA Cup by scoring nine goals in their last two matches.