3 things you need to know about Sunday's Premier League action

Sideline scuffles, missed penalties and head injuries - the four fixtures on Sunday's Premier League agenda had it all. 

Push came to shove as Jose Mourinho and Arsene Wenger renewed their rivalry at Stamford Bridge, a remarkable performance from David de Gea allowed Manchester United to earn three points against Everton, and Christian Eriksen lifted Tottenham to their first league win since August.

Here are three things you need to know about Sunday's Premier League action:

Chelsea drops Arsenal as tempers flare between Mourinho, Wenger

So intense was the atmosphere ahead of Chelsea's clash against Arsenal that the visiting supporters took a page out of their side's midweek Champions League match versus Galatasaray and delayed kickoff by setting off flares outside Stamford Bridge.

The carried over to the sidelines, where Jose Mourinho and Arsene Wenger's war of words took a physical turn following an atrocious challenge from Gary Cahill on Alexis Sanchez.

[Courtesy: Sportsnet]

Earlier this week, Mourinho claimed he didn't see the need to apologize for referring to Wenger as a "specialist in failure" last season, a comment intended as a response to Wenger's assertion Mourinho "feared failure."

On the actual pitch, it was Eden Hazard who opened the scoring on a penalty, which was awarded after he successfully dribbled past Santi Cazorla and Calum Chambers before being clipped by Laurent Koscielny.

In an all-too-familiar scene, Diego Costa added Chelsea's second goal of the match in the 78th minute after controlling a precision-perfect aerial pass and chipping the ball over Wojciech Szczesny.

Costa and Cesc Fabregas are genuinely establishing themselves as one of the most lethal duos in European football.

Also of note was the head injury suffered by Thibaut Courtois in the 10th minute, when he collided with Sanchez and was left sprawled out on the pitch, bleeding out of his right ear. Courtois continued to play for another 13 minutes before being replaced by Petr Cech, inevitably adding fuel to the fire over concussion protocol.

After the final whistle, however, Mourinho downplayed Courtois's injury, saying the Belgian 'keeper was sent to the hospital as a precaution and that it's "nothing to be too much worried about."

More than anyone, it was Arsenal's attack that look concussed throughout the match as they accomplished something the club hasn't done in 11 years.

Heroic performance from David De Gea gives Manchester United 3 points against Everton

If Manchester United can continue to get the type of performance from David De Gea they got during their 2-1 win over Everton, they may have an actual shot at competing for a Champions League berth.

De Gea thwarted five of Everton's six shots on target, including a diving right-handed stop on a penalty from Leighton Baines, who carried a 14-of-14 record coming into the match, having never missed from the spot in his Premier League career.

If that wasn't impressive enough, De Gea made two miraculous saves in the closing minutes of the match to preserve United's lead.

First came a massive denial on Leon Osman:

Then came one of the saves of the season on a powerful shot from Bryan Oviedo:

To say De Gea was humble about the save would be an understatement.

At the other end of the pitch, Angel Di Maria proved his £59.7-million worth by opening the scoring with a composed finish in the 27th minute, while Radamel Falcao scored his first goal since arriving at Old Trafford.

United's overall performance was arguably their best of the season, and after the match Louis van Gaal echoed the thoughts of those who believe the club can compete for the Premier League title.

"We are not playing good but we are already fourth in the table," Van Gaal said. "What is coming when we are playing well?"

Tottenham defeat Southampton as Mauricio Pochettino takes on former club

Players are often encouraged to avoid celebrating goals against their former clubs, but Mauricio Pochettino illustrated that such a rule also applies to managers in Tottenham's 1-0 win over Southampton.

Pochettino, who arrived at White Hart Lane from St. Mary's Stadium over the summer, decided against celebrating the match's lone goal when Christian Eriksen opened the scoring in the 40th minute. Instead, the Argentine manager opted to calmly walk back towards his seat on the bench with his hands in his pockets.

Speaking of Eriksen's goal, it was a fantastic way of finishing off an excellent passing sequence as Emmanuel Adebayor and Nacer Chadli combined to feed the Danish attacking midfielder a ball that only needed two touches before finding the back of the net.

[Courtesy: Reddit user "arcisal"]

The final whistle marked the end of an impressive streak for Southampton, who had won their past six fixtures in all competition and past four Premier League matches.

It was also fitting Eriksen was the one to end the Saints' run of form.