In the end there were fireworks being let off from the stand behind Filip Jörgensen’s goal and a few too many sirens sounding in Chelsea’s area. It was extraordinary to see Servette still plugging away deep into added time and, while Thomas Häberli’s side fell short of beating the £1bn project to a spot in the Europa Conference League, an unlikely upset would have been within reach if Timothé ­Cognat’s bending shot had found the net during the dying moments.

As it was the midfielder’s effort swerved just wide, sparing Chelsea the humiliation of being dragged to extra time by the side sitting seventh in the Swiss Super League. Even so, there was something deeply alarming about the manner of the ­implosion from Enzo Maresca’s second string after Christopher Nkunku’s early penalty put them 3-0 up on ­aggregate. Contriving to lose 2-1 on the night required a performance of bewildering lethargy and, although Chelsea could increase their many attacking options by signing Jadon Sancho and Victor Osimhen on ­deadline day, their development is likely to remain bumpy until they sharpen up without the ball.

Thwarting counterattacks remains a weakness, particularly with Enzo Fernández continuing to look ponderous in midfield, and it is not a surprise that Maresca wants a new centre-back given that Chelsea have conceded six goals in his first four matches in charge.

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“I think the first half an hour was comfortable and we had three or four chances to make it 2-0,” the head coach said. “Then we concede and it’s normal to suffer a little bit. I was very worried about this game. For them, it’s probably their biggest game of the season. This kind of game, you have many things to lose and not many things to win. This is why I was so worried before the game.”

The initial concern for Maresca was how his players would fare on a pitch badly damaged by a fungal infection. The danger about taking a 2-0 lead from the first leg for granted was clear, not least because Servette had created chances even in defeat, and there were immediate signs that the surface would pose problems for both sides.

Maresca made eight changes after last Sunday’s 6-2 thrashing of Wolves and he would see some crisp touches from the supporting cast at first. Fleeting promise came from Mykhailo Mudryk, starting a third successive game despite being hauled off at half-time against Wolves. Eager to impress, the winger would make his mark when he won a penalty after being caught by Keigo Tsunemoto. The tie seemed over when Nkunku beat Joël Mall from 12 yards.

Yet there was precious little consistency from Mudryk in general play and it was not long before Chelsea’s frailties surfaced. Their defending was from convincing and when Servette equalised midway through the opening period it was hard not to point the finger at Fernández and Kiernan Dewsbury-Hall for allowing Dereck Kutesa to surge through midfield before finding Jérémy ­Guillemenot, who drilled a low shot beyond Jörgensen after eluding Benoît ­Badiashile and Renato Veiga.

Chelsea’s composure evaporated before half-time. Nkunku and Noni Madeueke had chances to restore the lead but Jörgensen would have to make a sharp stop from the lively Kutesa.

The ball was coming back at ­Chelsea too much, a pattern exacerbated by Marc Guiu repeatedly ­losing his duels with Servette’s centre-backs. The 18-year-old striker made one chance for himself with some determined play but he does not look ready to be Nicolas Jackson’s deputy this season. More depth is needed. ­Chelsea will be intensifying their efforts to sign Osimhen from Napoli.

Chelsea had further chances, with Mall denying Mudryk after a thrilling burst from the winger, but they lacked control and failed to read the room. Roared on by their fans, Servette had hope when they took advantage of some soft defending with 18 minutes left. Enzo Crivelli, who made a difference after coming off the bench, had too much time to head a cross from another substitute, Miroslav Stevanovic, past Jörgensen, whose positioning at his near post looked suspect.

Maresca instantly turned to Cole Palmer. Chelsea livened up, Jackson having a goal ruled out for offside after coming on and Palmer hitting the bar, but their defence remained vulnerable. They could have conceded when another cross fell to Gaël Ondoua, whose shot was charged down.

The sight of Veiga being booked for time-wasting before a throw-in summed Chelsea up. They were mightily relieved when the final whistle confirmed their place in Uefa’s third-tier competition.