After Antonio Conte led Chelsea to their fifth Premier League crown in his first campaign, Pep Guardiola and José Mourinho embark on a defining 2017-18 season. Defining because the pair were granted a free pass last term. However, Conte’s feat casts a harsh light on how poorly Guardiola and Mourinho performed. Guardiola guided City to an unconvincing third and Mourinho took United to a lowly sixth. As the positions suggest, neither manager was able to mount a serious tilt at the title and thus their respective employers have to find excuses for them and succour from elsewhere.

The City chairman, Khaldoon al-Mubarak, pointed to the rebuilding job his man began, while Mourinho’s two-trophy return, which included the prize of Champions League qualification for claiming the Europa League, was enough for Ed Woodward, the United executive vice-chairman, to move on.

Now, they have to achieve more. The minimum requirement is that Guardiola and Mourinho ensure their team challenge for the title until May. If not, one or both may find themselves out of a job.

Chelsea should be viewed as favourites, despite the bookmakers awarding City the status. Whatever, it is difficult to look beyond a big four of the champions, the two Manchester clubs and Tottenham, last season’s runners-up, in the search for potential champions.

At Chelsea, Diego Costa has become persona non grata and will leave. He is a sizeable loss to Conte’s cause given the Brazilian’s edge and a strike-rate of 20 goals in 35 Premier League appearances last year, which followed 20 in 26 in the 2014-15 title-winning season.

In Costa’s place is Álvaro Morata, bought from Real Madrid for a club record £70m. The test is whether the 24-year-old can be a classic Chelsea Premier League centre-forward in the mould of Costa and Didier Drogba. Last season, Morata scored 15 in 26 appearances – 14 were starts – that totalled 1,334 minutes, an impressive average of one goal every 88.9 minutes. Morata, almost 6ft 3in, also scored the most headers in La Liga.

At City, Guardiola has splurged £199.79m on five players. Four of these are in defensive positions – Ederson, the new No1, and the full-backs Kyle Walker, Benjamin Mendy and Danilo, the latter also being a stop-gap holding midfielder. Bernardo Silva signed for £43.6m and joins Guardiola’s ever-burgeoning rank of attacking players. This also numbers Kevin de Bruyne, David Silva, Leroy Sané, Sergio Agüero, Gabriel Jesus and Raheem Sterling. The old joke about Arsène Wenger adding another No10 to his Arsenal squad when in doubt might apply to Guardiola and forwards.

Following last season’s travails, City’s campaign will depend on how well a leaky defence is tightened up. Guardiola’s summer spend is yet to include a centre-back despite this being a problem position. Currently, Vincent Kompany is the only established first-choice centre-half and he has been injury plagued in recent seasons. The captain’s two potential partners are the yet-to-do-it John Stones and the underwhelming Nicolás Otamendi. Tosin Adarabioyo is the only other recognised central defender and he is 19 and unproven.

Mourinho’s recruitment has taken in striker Romelu Lukaku, centre-back Victor Lindelöf and midfielder Nemanja Matic at the cost of around £146m. At the transfer window’s start the 54-year-old identified Lukaku as the prime target. After Zlatan Ibrahimovic’s serious knee injury, Mourinho decided Lukaku’s 88 league goals since 2012 – only Agüero has more in that time– made him the ideal spearhead.

Yet might Matic be the recruit that tips the title away from Chelsea and into United’s grasp? His significance can be read from Mourinho describing the midfielder as a genius following his debut in the 2-1 friendly win over Sampdoria. It remains a puzzle why Conte allowed Matic to be sold to United.

His arrival means Paul Pogba will no longer be asked to operate on the peripatetic basis that had him flitting between No6 and No8 and even, at times, No10. Pogba can concentrate on being the surging midfielder the manager wishes, though after United scored a meagre 54 goals – the poorest of last season’s top seven – this has to improved or it will not matter how the Frenchman plays.

Mourinho, who still wants to add a forward, has talked up Tottenham as challengers as they have kept all the players Mauricio Pochettino wants to retain. Yet the manager has, in turn, failed to freshen up his squad - recently he stressed the need to do so to ensure the competition that will help Harry Kane, Dele Alli and company elevate their game. Even if this changes Spurs are unlikely to better their rivals’ strengthening. Chelsea have also added Tiemoué Bakayoko (for £39.7m) and Antonio Rüdiger (£34m), so for Tottenham to finish second again would represent a small triumph.

For Watford, Burnley and Swansea City, the three clubs that finished last year 17th, 16th and 15th respectively, their cause for celebration will surely be if they once more avoid the drop. Watford have a seventh manager in three years in Marco Silva, and he oversaw Hull City’s relegation. Sean Dyche managed to keep the Clarets up for the first time in the Premier League but bringing in just Phil Bardsley, Jon Walters and Jack Cork suggests they will repeat their struggle. And if Gylfi Sigurdsson moves to Everton Swansea will earn a £50m fee but lose his playmaking abilities and last year’s nine priceless finishes. The promoted sides – Brighton & Hove Albion, Huddersfield Town and Newcastle United may – also be in the dogfight at the bottom.

At both ends of the division it promises to be a riveting watch.