The Spanish international headed his side into the lead to put Manchester United 2-0 up in the first half.

What a difference a season can make.

Last term, Manchester United struggled throughout large spells and are now without European football for the first time in ages. Meanwhile, Liverpool were close to clinching the Premier League title, and, despite having to settle for second-place, had the chance to compete in the Champions League, only to be knocked out and will now have to try their luck in the Europa League instead.

However, this season, the tables appear to have been reversed. After a shaky start, the Red Devils are now back on track whilst the Reds, after the sale of talismanic attacker Luis Suarez, appear to have lost their way and are struggling even to remain in the top half of the table.

Given the significance of the clash between these two Premier League giants, there were plenty of talking points early on.

In the first half, former Chelsea man Juan Mata put his side 2-0 ahead with a headed effort:

 

This got people buzzing, and not just due to Liverpool's struggles at the back. Rather, the question for many became...should it have counted? Was the Spanish star offside?

Check out some of the reactions below.

A funny look at it, perhaps?

 

 

On a serious note, here's what ESPN FC and Sky Sports think: