Manchester United vs Liverpool: Forget Alexis Sanchez and Mo Salah, Antonio Valencia and Andrew Robertson hold the key today

IT is the shoot-out between the two fiercest rivals in the Premier League.

A showdown between two clubs whose fans get almost as much pleasure when their sworn footballing enemies lose as when their own team wins.

And, with the title effectively wrapped up and heading to the Etihad, a clash which will do much to decide who is best of the rest.

So where will the battle be won? Will United be able to shackle the terrible trio of Mo Salah, Roberto Firmino and Sadio Mane?

Will United’s own terrific triumvirate of Romelu Lukaku, Paul Pogba and Alexis Sanchez all get it together in the same game for once and prove too hot to handle?

Or will it come down to whether David De Gea shows again why he is the world’s best keeper, or Lorius Karius why he has steadily built a reputation as Jurgen Klopp’s No1?

Well all of them will have a part to play. Yet the decisive factor could be one of the unlikeliest of all – which of the full backs comes out on top.

In the red corner is Antonio Valencia, the United right back with the build of a middleweight boxer and the feet of an Olympic sprinter.

REDS' DERB-GLEE Liverpool have the edge over Man United going into derby… thanks to Salah and Oxlade-Chamberlain

In the yellow – or whatever colour they describe that garish, eye-shielding Liverpool away kit – is left back Andrew Robertson, a man some rate as the buy of the season.

With Liverpool’s aforementioned treble strike force in such great form, it’s a fair bet the United backline will be more compressed to snuff them out.

That will leave more space on the flanks. And few wing backs get forward to such devastating effect as Robertson, whose delivery is second to none and whose stock rises by the week.

Amazing to think he played second fiddle to Alberto Moreno, a man who views defending like a vegan does a pork chop, in the season’s early months.

Yet up against him is Valencia, so often the unsung hero in this team of all-stars, yet anything but in the eyes of Mourinho.

A year ago the United boss hailed him as the best right back in the world. Maybe that’s stretching it a little, but he’s certainly one of the Special One’s blue chip stars.

It’s no surprise that Mourinho tried to sign him in his days at Real Madrid, insisting then he saw a great full back in the making, and even less of a shock that he was knocked back.

The difference in the Valencia of now, as opposed to the man who filled Cristiano Ronaldo’s boots, is immeasurable.

How many times is he the man whose pace sees him get back to make a crucial interception, toe-in or clearance?

And going forward from deeper allows him more space, more overlapping runs, and room to get behind opponents without the need to beat them with a trick.

If he comes out on top in his personal battle with Robertson – and he isn’t second best in many – United will go a long way towards winning.

Just one thing, though. After Nemanja Matic’s late winner at Palace on Monday, Mourinho’s men don’t need to win to stay ahead of their bitter Scouse rivals.

If that magical Selhurst Park strike guaranteed one thing, it’s that this particular Old Trafford showdown will be anything but a free-flowing classic.

Not that it will matter one jot to either set of fans if their team DOES end the day with all three points.