The fabled romance of the FA Cup will be thoroughly put to the test on Saturday as one of the most potentially-explosive fourth rounds in years kicks off after mounting appeals for calm.

All eyes will be on Manchester United’s trip to Liverpool and Chelsea’s short hop across west London to Queens Park Rangers as the four clubs meet for the first since becoming embroiled in twin racism controversies earlier this season.

Sir Alex Ferguson this week called for United fans to be on their best behaviour when they travel to Anfield in the first collision between the bitter northwest rivals since the Luis Suarez affair.

“FA Cup ties are tense affairs at the best of times,” Ferguson wrote in a letter to United fans this week.

“Add in the fact that Manchester United against Liverpool is the biggest game around and it becomes even more so.

“Your support is vital to the team and, down the years, that has been especially true at Anfield.

“But please put the emphasis on getting us into the next round and giving the sort of support you are famous for – positive, witty and loud.”

Liverpool captain Steven Gerrard echoed Ferguson’s comments.

“Liverpool and Manchester United is a massive rivalry and, of course, there is going to be stuff in the newspapers and banter between fans,” Gerrard said.

“But it would be fantastic if, after the weekend, it is remembered for being a top game and, obviously, from our point of view, a Liverpool win.

But the enduring tribalism between the clubs – brought into sharp focus by the Suarez saga – suggests Ferguson and Gerrard’s pleas might prove to be futile.

Liverpool striker Suarez, who was banned for eight matches after a disciplinary tribunal found him guilty of racially abusing United defender Patrice Evra, remains suspended and will miss the tie.

But Ferguson is expected to have no qualms about pitching Evra into the Anfield bearpit despite the fact the French international has become a hate figure for many Liverpool fans who insist Suarez was innocent of wrongdoing.

Meanwhile, officials from QPR and Chelsea joined forces this week in an attempt to keep a lid on the acrimony surrounding their first meeting since an ill-tempered Premier League derby in October.

Rangers’ victory in a game in which Chelsea were reduced to nine men was largely forgotten after the allegations of racism made against Chelsea captain John Terry following the game.

Terry has since been hit with criminal charges following an alleged incident involving QPR defender Anton Ferdinand, and both men are set to line up against each other at Loftus Road on Saturday.

Ferdinand has reportedly sought the advice of Rangers owner Tony Fernandes about whether he should shake hands with Terry before kick-off.

QPR chairman Fernandes, meanwhile, issued a statement with Chelsea counterpart Bruce Buck, urging fans to make the fixture a “celebration of football”.

“We have discussed the issues surrounding this weekend’s FA Cup fourth-round tie at Loftus Road and we are both in total agreement that abuse and discrimination has no place in football or society,” the clubs said.

“Both clubs enjoy fantastic support. However, we would remind fans that while we want to hear their passion, it’s a fact that hatred and abuse is not what being a fan of Chelsea or QPR is about.

“The clubs will work together with the police to ensure that anyone using discriminatory or inflammatory language is identified and that the strongest possible action is taken against them.”

Friday

Watford v Tottenham, Everton v Fulham

Saturday

QPR v Chelsea, Liverpool v Man Utd, Blackpool v Sheffield Wednesday, Bolton v Swansea, Derby v Stoke, Hull v Crawley Town, Leicester v Swindon, Millwall v Southampton, Sheffield Utd v Birmingham, Stevenage v Notts County, West Brom v Norwich, Brighton v Newcastle

Sunday

Sunderland v Middlesbrough, Arsenal v Aston Villa