We may be entering the cold winter period, but the Premier League title race is only hotting up.

Liverpool took top spot last weekend with a 6-1 thrashing of Watford while Chelsea also announced themselves as contenders with a 5-0 demolition of Everton.

With perennial title-winner Pep Guardiola at the Manchester City helm and Arsenal currently embarking on a 16-match unbeaten run a winner is tough to call - only two points separate the four teams.

And that's discounting a Tottenham Hotspur side that are still unbeaten and welcomed Harry Kane - last year's Golden Boot winner - back from injury in the north London derby.

With so many clubs vying for top spot, an old adage hold more significance than ever before - the team leading after the Christmas period usually goes on to win the title.

The rule generally holds true - five out of the last seven champions have been at the top of the table as they enter the New Year: it was Arsenal who let their advantage slip twice, last season and in 2014.

So what makes being top at Christmas so vital?

One of the main factors is that the Christmas period is usually the busiest part of any season. All the Premier League clubs can expect to play three matches in the space of a week, making it arguably the most important seven days of any campaign.

It is the time where teams really feel the rigours of the first half of the season take their toll as rotation, fatigue and injuries come into play. Usually, the team that can survive the best over such a punishing period i the side best-equipped to win the league.

Whilst this year may hold even more significance: two of the teams at the top are reaping the rewards of not being involved in any European football. Both Chelsea and Liverpool finished outside of the European places last year and as such have no continental commitments.

It's certainly having an effect this year. Both Jurgen Klopp and Antonio Conte are free to choose their best lineups week-in, week-out with little need to rotate, and that has resulted in some incredible performances. They need to be careful, however. There are two reasons why they may come unstuck.

The first is that while consistently using the same players improves their understanding of each other, it can cause problems when other players need to come in. Should players like Diego Costa or Philippe Coutinho pick up an injury it could hugely effect the team as a whole and lead to dropped points.

On top of that, there may come a time when their rivals are no longer in Europe and focus solely on the league. Spurs may not make it out of the group stages while Arsenal often exit around March while the same could happen to Manchester City, making them likely to finish strongly.

In 2013/14 Liverpool - with an attacking team already drawing parallels to the current Reds squad - looked set for a first ever title win but lost out after dropping points against Chelsea and Crystal Palace. Manchester City, fully-committed to the league after a European exit to Barcelona, won their final five games to triumph.

This year's title race has a unique trait in that almost every club is currently managed by a title-winning manager. Klopp and Conte won multiple titles in Germany and Italy, Arsene Wenger has three Premier Leagues at Arsenal whilst Guardiola has won almost everything with Barcelona and Bayern Munich. And that's forgetting Jose Mourinho would could yet inspire a United charge.

All those managers have experience of what it takes to win over 38 games and know how important it is to head into the New Year on top. You can bet they will each fight tooth and nail to make sure it's them.

The title race may be hotting up, but when the New Year comes around, it'll be at boiling point.