Five things to watch out for in the Premier League

All eyes will be on Stamford Bridge this weekend as Chelsea start life without Jose Mourinho again. However, as the Premier League enters the busy festive period, there are plenty of other talking points to get excited about, including a defining match for title hopefuls Arsenal and Manchester City.

Were Chelsea's stars refusing to perform for Mourinho?

It's impossible not to start with the Blues.

After making the worst ever start to a title defence in England, 'the Special One' was finally sacked after the 2-1 defeat to Leicester City, which was made all the worse by the fact the Foxes have remarkably move to the top of the league under the guidance of Cladio Ranieri – whom Mourinho has often maligned in the past.

Staggeringly, Chelsea are only one point above the drop zone ahead of this weekend's matches, meaning their clash with second-bottom Sunderland is a genuine relegation six-pointer. Should the Black Cats pile on the misery at Stamford Bridge with a win on Saturday, then they would draw level on points with the reigning champions.

"Our job on Saturday is to try and continue that cloud Chelsea are under," admitted Sunderland manager Sam Allardyce, and it will be thoroughly intriguing to see how the Blues' players face up to Big Sam's side.

As Mourinho's position became increasingly vulnerable, speculation intensified that the Portuguese had lost the support of the dressing room and that certain members of the squad were no longer willing to perform to their capabilities for him. Technical director Michael Emanalo has confirmed as much, admitting there was a "palpable discord between manager and players".

With Eddie Newton and Steve Holland set to take charge of the side as Guus Hiddink finalises his return as interim manager, don't be surprised to see the likes of Eden Hazard, Cesc Fabregas and Diego Costa return to form.

Clash of the Titans at the Emirates

With the reigning champions in utter turmoil, the Premier League title race is the most open it has been for years. All of the fancied teams have shown their frailities; so much so, Leicester City are currently top of the pile. There is still an expectation that Arsenal or Manchester City – second and third, respectively – will eventually flex their muscles, and the two face each other on Monday night in North London.

Depending on how Leicester get on at Everton – more on that later – either side would go top with a victory, in what would surely be a huge psychological boost.

Throughout Arsenal's continuing 12-year wait for the title, one of their main problems has been their form against rivals for the crown. Arsene Wenger has often refused to adapt his playing philiosophy, but last year appeared a breakthrough as the Gunners won 2-0 at City thanks to a defensively-minful, counter-attacking display.

In fairness to Wenger, the Frenchman may be better off going on the attack at the Emirates Stadium, as City have looked terribly vulnerable in the absence of captain Vincent Kompany.

The Belgian will be one of a host of stars missing for both sides, alongside the likes of Santi Cazorla, Jack Wilshere, Pablo Zabaleta and Samir Nasri. However, key forwards Alexis Sanchez and Sergio Arguero could return for either team.

City manager Manuel Pellegrini's week has been made even tougher with further reports he is to be replaced by Pep Guardiola in the summer – a fifth loss of the season will only make the Spaniard look even more appealing to the Etihad hierarchy.

Vardy and Mahrez continue battle for player of the year

Alongside Chelsea's demise, the story of the season has undoubtedly been Claudio Ranieri's Leicester City. Despite having pulled off a great escape from relegation under Nigel Pearson last term, many pundits had tipped the Foxes to go down this season after the appointment of the Italian. Certainly nobody predicted them to be top with almost half the campaign played.

One of the major factors of their escape from the drop last season was the form of forward Jamie Vardy and winger Riyad Mahrez, and the duo have kicked on to another level entirely under Ranieri.

Algeria international Mahrez inspired the 2-1 victory over Chelsea last Monday, delivering a superb cross for Vardy's opener, before scoring an exceptional second. The 24-year-old has been involved in more goals than any other player in the Premier League, netting 11 himself and assisting a further seven.

Former Fleetwood forward Vardy, meanwhile, has broken the record for consecutive goals, and only BVB Dortmund's Pierre-Emerick Aubameyang has scored more goals in the top five European leagues.

The pair are undoubtedly the players of the season so far – with Arsenal's Mesut Ozil perhaps the only realistic contender – and the only argument as things stand is which one should win the ultimate crown.

Leicester travel to Everton on Saturday in what promises to be an extremely exciting fixture. Vardy and Mahrez should have plenty of opportunites to strengthen their claim for individual honours.

The Mauricio Pochettino derby

Eyebrows were raised in the Premier League when Southampton decided to somewhat harshly sack Nigel Adkins and replace the man who won them promotion with a relative unknown in former Espanyol manager Mauricio Pochettino.

However, the decision proved a masterstroke, as the Argentinian easily guided the Saints to safety, before helping establish Southampton as a team which could compete for the European places. His work on the south coast prompted a move to Tottenham where – after a slightly difficult first season – he is starting to work his magic.

Pochettino takes Spurs to his former club on Saturday, and both sides are in need of victory.

The hosts have gone five matches without a win, slipping into the bottom half of the table after a promising start to the season, leading to manager Ronald Koeman to admit results need to change if he wants to keep his job.

"There is always pressure and I’m used to that. The expectations for Southampton are much higher than last year. Our target is very high. If we cannot reach that at the moment, you are always under pressure," he said.

Tottenham, meanwhile, lost their first match since the opening day of the season against Newcastle last week, and are on a run of three league matches without a win.

Pochettino needs three points against his former club to kick-start the North Londoners challenge for the top four.

Differing atmospheres at strugglers

What a difference a week can make in football.

Following Newcastle's 5-1 thrashing at the hands of former manager Alan Pardew's Crystal Palace, the Magpies seemed destined for relegation, and Steve McClaren was staring at the sack. The players didn't seem to care and reports followed of clashes at training as McClaren aired a few unwelcome home truths.

Whatever the former England manager said obviously worked as Newcaslte recorded eye-catching wins over Liverpool and Tottenham in the space of seven days, and the modest McClaren gave all the credit to his players.

"There have been so many times when I have gone in at half-time and the dressing room has been silent. I was angry at the goal, but the players were fabulous at half-time. It was so vocal, such a determination in the players not to go down the same path as they usually do," he said.

However, nothing seems to have changed at Aston Villa – who travel to St James' Park on Saturday. Despite replacing Tim Sherwood with Remi Garde last month, the club have made the worst ever start to a Premier League season, sitting bottom of the table with only six points.

Garde has yet to win a match in charge, and some of his players appeared to give up in the build up to the second goal in the 2-0 defeat to Arsenal last week.

The Frenchman faces a monumental task to turn Villa's fortunes around – it could be time to take a leaf out of McClaren's book and tell his squad some things they might not want to hear

Rob Conlon