Five reasons why Chelsea's Premier League title defence has failed
On Sunday, Chelsea face the team that will eventually inherit their status as Premier League champions. Manchester City's historic pace has blown away the chasing pack and Pep Guardiola is poised to win his seventh league crown in nine years as a coach.
Things were so different in last season's corresponding fixture, when Antonio Conte's men dramatically came from a goal down to beat City 3-1 at the Etihad Stadium in December 2016 in the midst of a 13-game winning streak that propelled them to the title.
Plenty has undermined Chelsea off the pitch since then, but what has changed to make them a shadow of their former selves on it?
ESPN FC takes a look at the five biggest reasons for Chelsea's decline.
1. The old defensive solidity has gone
Gary Cahill and David Luiz, two of Chelsea's back three at the Etihad last season, are no longer regular starters.
This is largely by design; Andreas Christensen has forced his way into Conte's team on merit, barely putting a foot wrong until the past two matches, while Antonio Rudiger's speed is regarded as a better complement to Marcos Alonso.
But collective chemistry is key to a successful defence and it's clear that shuffling the combinations has disrupted things. Chelsea are actually just two clean sheets shy of last season's Premier League total (16), but when things do go wrong at the back, they more frequently go very wrong.
Chelsea have conceded two or more goals in seven of their 28 matches, the same number of times as occurred in the whole of last season.
They are also giving up 10.1 shots per game compared to 8.5 in 2016-17 -- a statistic that speaks just as much to a more porous Chelsea midfield in the wake of Nemanja Matic's summer move to Manchester United.
2. Conte's 3-4-3 has gone stale
By the time the rest of the Premier League realised the strengths and weaknesses of Chelsea's unorthodox system, the title was virtually secured. This season the element of surprise has gone and Conte has lost his tactical edge.
Other managers have followed his example, particularly when facing Chelsea. Indeed, the Blues have come up against opponents playing a three-man central defence in 11 of their 28 Premier League matches this season, with wildly varying results.
Irrespective of whether they match up in terms of formation, most teams are now wise to the fact that they need to press Chelsea's back three aggressively, cutting off easy passing angles into midfield and forcing their defenders into either hopeful long balls or mistakes.
This has shaken Chelsea players' confidence in what Conte calls his "idea of football" in turn, making them less able to execute the fast transitions and switches of play to the flanks that the system requires. It is a vicious cycle that has underpinned their worst performances.
3. Diego Costa has not been replaced
Diego Costa was the main reason why Chelsea went into 2017 six points clear at the top of the Premier League. In addition to being the perfect "point of reference" for Conte's system he scored 14 goals in 19 matches in the first half of the season, of which five were game winners and two were equalisers.
His acrimonious return to Atletico Madrid left formidably big shoes to fill and £58 million arrival Alvaro Morata has struggled mentally as well as physically with the burden.
Hampered by hamstring and back issues, Morata has scored just five goals in 26 Chelsea appearances across all competitions since the end of September. His shot conversion of 15.6 percent in the Premier League (10 goals from 64 shots) is also inferior to Costa's scoring rate of 18 percent (20 goals from 111 shots) last season.
But the problem is bigger than Morata. Chelsea's attack is a shadow of what it was, averaging 1.78 goals per game in the Premier League and converting just 10.9 percent of shots. In 2016-17 those numbers were 2.24 and 14.6 percent.
Of the current squad only Eden Hazard, Willian, Alonso and Victor Moses have matched, or are on course to surpass, their goal tallies from last season.
4. Chelsea have a creative deficiency
Cesc Fabregas is having a strange season. He has already started more Premier League matches (17) than he did in the whole of 2016-17 (13) and is averaging 2.9 key passes per game, up from 2.1 last term. Yet he has just four assists to show for his efforts, eight fewer than he managed on the run to the title.
That can partly be explained by the fact that Chelsea are converting fewer chances than last season, but precious little creation is coming from elsewhere.
No player in the squad has more than six assists and the fact that defender Cesar Azpilicueta is at the top of the list does not speak highly of his more attack-minded teammates. Pedro, who directly set up nine goals in 2016-17, has provided just two this season.
The struggles of others have too often left Hazard with the burden of being the chief scorer and chief creator in the team. As a result, Chelsea have at times been easier to shut down than Premier League champions should be.
5. Conte has no Plan B
Sunday's defeat to Man United was the first time this season that Chelsea had lost a Premier League match that they led. They have always been good front-runners under Conte and it is just as well, because they have shown precious little ability to salvage games that are going against them.
Of the seven league matches in which Chelsea trailed at the 75-minute mark last season, the full-time record stood at one win, one draw and five defeats. These numbers are identical for 2017-18, but Conte's problem is that his team have found themselves in the situation seven times in 28 games rather than 38.
Conte's substitutions are typically cautious, late (41 percent of them coming on 75 minutes or later) and relatively inconsequential; only five of Chelsea's 50 Premier League goals have come from their bench and the man responsible for two of them, Michy Batshuayi, is now playing for Borussia Dortmund.
If they are to repeat last season's memorable win at the Etihad Stadium on Sunday, the evidence of this season suggests Chelsea will have to strike early.
Liam is ESPN FC's Chelsea correspondent. Follow him on Twitter: @Liam_Twomey.