Chelsea manager Frank Lampard enjoyed a memorable win over his former Blues boss Jose Mourinho as his side beat Tottenham Hotspur 2-0 in a fiery London derby overshadowed by racism allegations, while Manchester United again succumbed to one of the Premier League's lesser lights as it lost 2-0 to bottom-of-the-table Watford.

Liverpool remained 10 points clear at the top of the table without playing a match -- it won the Club World Cup for the first time thanks to a 1-0 victory over Brazilian side Flamengo in Doha on Saturday -- when second-placed Leicester lost 3-1 to Manchester City.

Here are five things we learned from the Premier League weekend:

Lampard comes of age

After four defeats in its previous five league games, Chelsea made the short trip across London to face Tottenham beset by doubts for the first time in Lampard's debut season in charge.

That run stoked fears about Lampard's lack of experience in just his second season as a manager, with Chelsea fans hoping he could steer them back to the glory days he enjoyed as a player.

But Lampard gave the perfect response, fittingly against the manager who was his mentor when he shone in Chelsea's midfield.

Changing from his usual 4-3-3 formation to a 5-2-3 system, Lampard completely out-witted Mourinho, who was powerless to counteract the switch as Willian's double confirmed Chelsea will spend Christmas Day in a morale-boosting fourth place.

United struggles with the ball

Manchester United is a Jekyll-and-Hyde team, able to compete against the top sides in the Premier League but with a bizarre blind spot against lower-ranked teams.

It was a familiar tale at Vicarage Road on Sunday, with United enjoying the lion's share of possession against Watford but leaving empty-handed after two defensive mistakes in a 2-0 defeat.

United has taken just three points this season from seven matches against Southampton, West Ham, Newcastle, Bournemouth, Aston Villa, Everton and Watford.

But it has beaten Chelsea, Tottenham, Manchester City, and held Liverpool to a draw.

Under Ole Gunnar Solskjaer's management, United has won 73 percent of the Premier League games in which it has had less possession than its opponents, compared to just 36 percent when it has enjoyed more.

But after the Watford match the Norwegian manager, whose team is eighth in the Premier League and seven points off the top four, said the game hinged on a lack of quality, not possession.

“There's many different reasons for the outcome of a game of football,” he said. “You create chances, you don't score goals.... It's got to start with more urgency. We've got to play better.”

Man City down but not out

Liverpool may be well on its way to ending a 30-year wait to be crowned the champion of England again but Premier League title-holder Manchester City showed its determination to stay in contention with a win over Leicester that ended the Foxes' 11-match unbeaten run.

Kevin De Bruyne was again in superb form as goals from Riyad Mahrez, Ikay Gundogan and Gabriel Jesus saw City to victory after Leicester striker Jamie Vardy had opened the scoring at the Etihad Stadium.

City, for all it is within a point of Leicester, is still 11 adrift of Liverpool and has also played one more game than the Reds.

But City manager Pep Guardiola insisted: “If we play like we did tonight we can compete with everyone.

Arsenal's poor form continues

With Arteta not officially taking charge of his first Arsenal match until the Boxing Day trip to Bournemouth, interim head coach Freddie Ljungberg oversaw yet another below-par display from his side.

The Gunners looked the more likely side to score on Merseyside but lacked cohesion all over the field and had to settle for a point, making it just one win in 13 matches in all competitions.

Arsenal did at least manage to test Jordan Pickford - the England international doing well to keep out Pierre-Emerick Aubameyang in the second half - with the Toffees rarely troubling the opposition defence.

Racism mars Premier League again

There was little Christmas cheer for Tottenham, which may have to answer for the behaviour of their fans amid claims Rudiger was racially abused and an object was thrown at Chelsea keeper Kepa Arrizabalaga.

A fan was seen directing a 'monkey gesture' at Rudiger and three announcements over the tannoy that “racist behaviour from spectators is interfering with the game” painted a bleak picture of the latest racist incident to scar European football this term.

( With inputs from Omnisport )