The Premier League has been somewhat of a two-horse race over the past few seasons as Liverpool and Manchester City have been a class above the rest, but the tide began to turn towards the end of the last campaign.
Manchester United finished second in the league for the first time since Jose Mourinho was in charge, and Chelsea beat Pep Guardiola's City in the final of the Champions League as the playing field was levelled.
The current Premier League season has started off in fine fashion, and the title race looks set to be as exciting as ever with City, United, Liverpool and Chelsea all staking a claim as to why they should be taken seriously in this years battle.
However, United have seen a major dip in form, and Ole Gunnar Solskjaer's side risk falling behind the rest of the pack, with Chelsea ready to lead the charge.
United went from being unbeaten to losing three times in a week across three different competitions, and they were arguably all games that Solskjaer would have expected to win, let alone draw.
They had Cristiano Ronaldo to thank for his last minute heroics on Wednesday against Villarreal as United beat the Spanish side 2-1 in the Champions League to get them back to winning ways at home, but Solskjaer's side were second best for a large portion of the tie highlighting that there is still a lot of work to be done.
The highs of Ronaldo's second debut for the club were quickly masked by a 2-1 defeat to Young Boys in the Champions League, and although United kept up their impressive league record away from home with last-gasp winner against West Ham, they lost twice at Old Trafford in the space of four days.
West Ham got some revenge by knocking United out of the Carabao Cup thanks to an early Manuel Lanzini goal, but it was their lacklustre performance against Aston Villa last Saturday in the Premier League that will be the main concern.
Solskjaer's side couldn't break down an organised Villa side, and Kortney Hause took full advantage as he headed the visiting side in front with two minutes to go, before Bruno Fernandes empathetically missed his penalty in injury time as United were defeated 1-0 at home again.
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There was something missing from United's game, and despite getting over the line against Villarreal on Wednesday, they need to resolve the situation fast as they face a gruelling run of Premier League games following the conclusion of the second international break in October.
Solskjaer's side host Everton this weekend, which will be tough enough in itself following their great start to the season under Rafa Benitez, but United's run of fixtures through October are particularly daunting.
United travel to Leicester on the first weekend back after the international break before hosting Liverpool at Old Trafford, and then face both Tottenham and Manchester City to complete a brutal three week period with a double-header of Champions League games against Atalanta sandwiched in between.
It will be over this three week period that we learn if United are serious title contenders this season, but if they continue their poor form heading into these crucial fixtures, it's likely they could slip well behind Chelsea and forfeit their Premier League challenge.
Chelsea also surrendered their unbeaten run last Saturday, but their 1-0 defeat came against a faultless City side as Guardiola finally got the better of Thomas Tuchel as the fourth time of asking.
The Blues also lost 1-0 in their tough Champions League clash away to Juventus on Wednesday but the difference is, Chelsea are level on points with United domestically after already facing Liverpool, Arsenal and City in their opening six games, but now prepare for what could be a golden run in the Premier League, and steer clear of their title rivals.
Four of Chelsea's next five Premier League opponents are yet to win in the top-flight this season, with recently promoted Brentford their only opponent to pick up all three points at some stage since the start of the campaign, and this will be an excellent opportunity for Tuchel to pose a faultless record heading into November.
Chelsea will host strugglers Southampton, Burnley and Norwich over the next month and travel to Newcastle and Brentford to make up the calendar for the near future, which is quite the contrast from United's difficult task.
Tuchel's side have Champions League duties to factor in themselves, but again they've lucked out relatively speaking, as a double header against Malmo fall between these dates and the Swedish team are considered the weakest side in their group after being thumped 4-0 by Zenit St Petersberg.
Chelsea could be well clear of United, and have the opportunity to push away from their other title challengers too, although Liverpool remain the only side to stay unbeaten so far.
Champions City will be hoping to retain their crown once more, but Guardiola will not be happy with how inconsistent his side is and unless they can get into their groove, it could be Chelsea's to lose.
If Chelsea do pull away, they could be tough to catch and if Solskjaer's form continues then pressure will mount on the Norwegian if they fail to compete with the best in the league.
United will face a similar run of games to Chelsea in December, but if they fail to keep up with Tuchel's side, their Premier League challenge could already be over by then.
