While the importance of the fixture has dwindled in recent times - in terms of its stature at the top end of the Premier League, at least - there is no denying that Manchester United vs. Liverpool is still arguably the biggest club game in world football.

England's two most successful sides, boasting a whopping 86 major trophies between them, face off at Old Trafford this evening in a clash that is expected to be watched by an audience of around 700m people.

That is the last recorded figure for this showpiece fixture, with close to a billion people tuning in to watch United's 2-1 win in the reverse meeting earlier this year, some 250m than the next best viewed match - the El Clasico bonanza between Barcelona and Real Madrid on the same day.

Ahead of the latest coming together, which promises to be a real classic for the neutral, Sports Mole picks out five big talking points concerning both teams.

1. Liverpool's Old Trafford hoodoo

The date is March 16, 2014. Luis Suarez has just latched on to Daniel Sturridge's scuffed shot, coming at the end of a decent passing move, before calmly slotting the ball past David de Gea and reeling away in delight. It was a memorable afternoon for Liverpool at the home of their arch rivals, which was made all the sweeter by the fact that the doubts over their title credentials, from the outside at least, had been increasingly growing.

This win took the Reds within four points of leaders Chelsea with a game in hand still to play, while opposition star Wayne Rooney described the result as a "nightmare". The importance of this fixture is that it is the only time the Merseyside outfit have avoided defeat at the Theatre of Dreams in their last eight visits.

United have often relied on slender victories on home soil to see off Liverpool, but more times than not they get the job done. Interestingly, there has not been a draw in this fixture at Old Trafford since the turn of the millennium in March 2000 - a run stretching back 17 matches.

2. Mixed start to campaign for both

At this early stage of the season, it takes just one result - negative or positive - to completely change the mood of the fanbase. Take Liverpool, for example, who kicked off their season with back-to-back wins before claiming a credible goalless draw away at Arsenal. A 3-0 thrashing at home to West Ham United prior to the international break has changed the complexion of things entirely, though, and now Brendan Rodgers is under some sort of pressure again all of a sudden.

It has actually been an identical story for the Red Devils who, without looking anywhere near their best, took six points from six in the opening weeks before slipping away somewhat. A goalless draw at home to Newcastle United, a poor result against a side who have badly struggled on their travels over the past 12 months, was followed up by a dramatic collapse against Swansea City last time out.

Louis van Gaal and Rodgers have both had two weeks to reflect on those potentially costly defeats, though in truth the outlook is still positive enough. Seven points from the opening five games is hardly title-winning form, but it is certainly enough to keep them in contention for the big prize come May.

3. Defensive records hard to read

Liverpool may have kept three clean sheets in their opening four games, a decent tally when considering they shipped nine in their final two games last term, but the defensive frailties were clear to see once more in that defeat to West Ham. A disorganised backline allowed the Hammers to score at will, which simply cannot be allowed to happen on Saturday evening.

The absence of Philippe Coutinho is a major blow for the Reds, yet it may just allow Rodgers to shuffle the pack a little and provide some additional defensive resilience in front of his frail backline. Joe Gomez and Nathaniel Clyne have settled well on the whole, despite recent high-profile criticism from Harry Redknapp, but it is now down to Martin Skrtel and Dejan Lovren to remain solid.

Again, it is a similar story for United in the opposite corner, having themselves recorded three shutouts so far in a record only blemished in their final outing before the two-week hiatus. Sergio Romero, solid enough in the early stages of his Premier League career, was at fault for one of the goals at the Liberty Stadium, while the backline as a whole was also badly exposed at times.

4. Mixed success in transfer window

No sport comes close to football in terms of its fickle nature, which is always best epitomised at this time of the year when the transfer window closes. When flying high on the back of those impressive opening results, much was made of Liverpool's shrewd business in the summer market.

In came the likes of Danny Ings, Roberto Firmino, James Milner, Gomez, Clyne and, perhaps best of all, Christian Benteke. The Anfield outfit now have an added dimension to them, but one defeat and all of a sudden this is a "bang average" side. While the jury may still be out on Rodgers's summer spending, serious questions have already been asked of opposite number Van Gaal.

The £36m capture of Anthony Martial - a figure only likely to rise in the coming years - marked one of the shock signings of this year's window. Particularly startling is the fact that the Dutchman allowed Adnan Januzaj, someone he has talked highly of this term, as well as Mexican forward Javier Hernandez, to depart on temporary and permanent deals respectively. Right now United appear to be a side in panic mode, but maybe - just maybe - Van Gaal knows exactly what he is doing.

5. Rooney closing in on more history

Finally, after firing home from the spot against Switzerland in midweek, the drawn-out talk of Rooney breaking Bobby Charlton's long-standing goalscoring record for the England national side can be put firmly to one side. The Three Lions skipper himself admitted that he was glad to be able to focus on other matters after achieving the feat, but it is now a similar story at club level.

Rooney is one off Denis Law's tally of 171 goals in third place, while only Charlton (199) and Jack Rowley (182) have scored more. A lot has been made of the former Everton man's barren scoring run in the Premier League - no goal in 10 stretching back to last April - but he is likely be given the nod once more up top by Van Gaal should he overcome an injury scare.

In goal, meanwhile, De Gea is in line for his first appearance of the campaign after the shambles of his summer-long transfer saga, which came to a rather embarrassing end. The Spaniard has failed to keep a clean sheet in any of his last seven 90-minute appearances in the league, and he comes up against a Liverpool side who are aiming to avoid going three games in succession without scoring in the top flight since March 2005.