Chelsea might not win the Premier League this season for various reasons, despite holding a three-point lead heading into 2015 - before capitulating against Tottenham - and an impeccable recent record of finishing the job when top at Christmas.

Manchester City have well and truly made this a two-horse race, managing various injury problems to reduce the gap, which had been eight points – the Citizens recently won nine successive games in all competitions. The Blues have squandered great opportunities to put themselves out of sight, primarily failing to dispatch of City's 10-men, and conceding a dramatic late equaliser at Old Trafford.

Chelsea have stumbled after an excellent start of 11 unbeaten games, including visits to the Etihad, Old Trafford and Anfield and beating Arsenal at home. This led to Chelsea becoming strong title favourites with bookmakers at just 1/4, yet they have now slipped to 4/6, with City moving from 13/2 into 6/4.

Chelsea may come to suffer from being overdependent on key players in their squad, particularly given they’ve currently been fortunate with injuries. Aside from Diego Costa’s temperamental hamstring disruption, there have been minimal, with their squad depth not truly tested yet. Mourinho has a strong core of players who all start when available: Cesar Azpilicueta, Gary Cahill, Diego Costa, Cesc Fabregas, Eden Hazard, Branislav Ivanovic, Nemanja Matic and John Terry. Back-up centre-half Kurt Zouma is ultimately unproven for all his talent, whilst Ramires and John Obi Mikel cannot match their midfield colleagues. However, the reserves have rarely been needed, whilst Chelsea have not had to cope without Eden Hazard, who has been outstanding recently.

Chelsea are the only English side left competing across all four competitions, meaning their squad strength will inevitably be more thoroughly examined as the season continues. Third-place chasers Manchester United, who have recently found outstanding form under Louis Van Gaal, have no European distractions whatsoever. This, combined with their superb attacking firepower, mean similarly to Liverpool last season their presence in the title race should not be discounted.

Manchester City, in contrast to Chelsea, have been extremely unfortunate with injuries to key players thus far this season. This has included coping without world-class centre back Vincent Kompany and outstanding striker Sergio Aguero for months amongst various problems.

The Citizens have managed admirably without an available striker in recent games, reigning in the Blues to being level on points. That they have managed this against a Chelsea side that started so well is of huge credit to them and must concern Blues fans. City are very much accustomed and familiar to winning the title from behind, having hauled into long-term leaders for both of their recent successes. Most famous in 2011-2012 they hold in an eight-point deficit, with just six games remaining, against Alex Ferguson’s Manchester United.

In summary the likely upcoming tests to Chelsea’s squad depth and managing European football, combined with the challenges of both Manchester clubs, suggest the title race is far from over. Though in Mourinho, Chelsea arguably have the best manager in the world, Manchester City’s ability to handle injuries and remain on their shoulders suggest this may go the wire. It is set to be the battle of the team who likes to win championships by leading from the front, versus the side who likes to win them by chasing from behind. Something has to give, and Chelsea's thrashing at the hands of Spurs recently strongly suggests they will blink first.