LONDON -- Chelsea may be an ever-changing entity these days, but Sunday's 3-1 defeat at West Ham United underlined how their inability to take chances remains a worrying constant.
The last striker to surpass 20 goals in a Premier League season for the Blues was Diego Costa in the 2016-17 campaign, which, not coincidentally, was the last time they won the league.
More recently, Thomas Tuchel inherited the problem from the previous head coach Frank Lampard, and he tackled it by making the Blues the most robust defensive team in Europe, securing an improbable 2021 Champions League triumph founded on defensive solidity.
The Blues brought in Romelu Lukaku that summer in a bid to cure the problem. As much as expected goals figures should always be taken as a guide rather than gospel, Chelsea's profligacy has been in plain sight for a while: in the 2020-21 league campaign, their xG was 62.9 but they scored only 58 goals -- compared with champions Manchester City's 83 goals (from 68.9), Manchester United's 73 (60.9) and Liverpool's 68 (68.3).
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Under Tuchel's successor, Graham Potter, Chelsea underperformed their xG by 7.4 during his reign -- the worst differential of any side since his appointment in September last year (21 goals from 28.4 xG).
The issue is now Mauricio Pochettino's to solve, and he was given a crash course in the detail here at London Stadium. Despite West Ham coach David Moyes admitting that "[Chelsea] were the better team for long periods," the Blues slumped to their first defeat of the season.
They had the game firmly in their grasp at 1-1 after recovering from a slow start to dictate the majority of the first half. After Nayef Aguerd had headed West Ham in front on seven minutes and Carney Chukwuemeka equalised with his first senior goal, the game turned on Enzo Fernández's missed penalty two minutes before the break. Hammers goalkeeper Alphonse Areola flew to his right to repel a weak Fernandez effort, and after Chukwuemeka limped off, Chelsea never re-established control of the match in the second half.
Pochettino opted to replace Chukwuemeka with Mykhailo Mudryk rather than new £115 million British-record signing Moisés Caicedo, who presumably was not deemed fit enough for more than a 30-minute outing given he came on for Ben Chilwell on the hour mark. By that stage, Michail Antonio showed Chelsea what clinical finishing looks like, collecting James Ward-Prowse's pass -- chalk up two assists for the £30m man on debut from Southampton -- before thrashing a shot past Robert Sánchez from the edge of the box.
Aguerd was deservedly sent off for a lunge on Nicolas Jackson after 67 minutes, meaning Chelsea continued to monopolise possession but then they had done all afternoon regardless: They had 78% of the ball in the first half, it was still above 70% by the time Aguerd departed and the final figure stood at 75%.
Yet they could not translate that superiority to the scoreline. Chelsea amassed 17 shots to West Ham's 12 but they managed one shot on target after Fernandez's penalty miss -- and that came in the second minute of stoppage-time as substitute Noni Madueke's shot was deflected.
The chances dried up but they had already created enough threatening moments to put the game beyond West Ham long before. Instead, this became one of those structured, resilient defensive performance Hammers boss Moyes has made a career out of.
"Teams like us, we need to get the right balance," Pochettino said. "I think today there were a few actions we didn't manage well and we concede. We create many chances and we did well in the first half. We should have won the game with our first half.
"In the second half with another isolated action, we concede again. To find the space to create clear chances [is difficult] but overall it is this type of game that is difficult to explain. You had the possession, you create and maybe you were the better side but in the end you lose."
There was talk last season that Chelsea's travails in front of goal became a psychological problem, but Pochettino insisted he has not inherited some sort of collective mental block.
"No, I cannot see nothing like this, for sure. This is a new team, new players. I am not feeling what happened the last few years here," he said.
It is inevitable, of course, that Chelsea need time to resemble a cohesive team. While £850 million (just more than $1 billion) can sign a plethora of talented individuals, only time and work can make a team. Those component parts must eradicate mistakes.
Fernandez, a £105.8m signing in January, looked unconvincing from the spot, while Caicedo, who replaced him as the most expensive player in England, marred his debut by conceding a late penalty that Lucas Paquetá converted to prompt a mass exodus from the travelling Chelsea fans.
Chelsea cannot escape the problems in front of goal, however, nor can Pochettino, despite the dramatic and far-reaching change in personnel. The team can count more captains (three) than goals this season (two): Reece James' injury left Chilwell to take the armband before it was passed to Thiago Silva, who also ended up as skipper in last's week draw vs. Liverpool.
In a sign of how bizarre this game was, Nicolas Jackson led the line with flashes of quality and purpose, working diligently without the ball to press in the Pochettino style. Raheem Sterling was a regular menace, triggering panic in the West Ham defence on multiple occasions and yet, they needed a midfielder to find the net here after defender Axel Disasi scored their only goal against Liverpool.
"Dominating a game at a ground like West Ham's you have got to take your chances, this is the Premier League and it will come back to haunt you," Sterling told Sky Sports.
Cynics will argue Chelsea could just go and sign another striker but that is a tricky proposition given what does it say to Jackson and Christopher Nkunku, whose season is likely to start in the New Year following knee surgery.
Pochettino suggested on Friday that Armando Broja could fill the void, but he has been out of action since December following knee surgery of his own, and for all his promise, the 21-year-old has only ever scored seven league goals. Yet from somewhere amid all the upheaval, Chelsea's ability in front of goal still needs to change.