For a manager usually so astute with his tactical decisions, Jose Mourinho will be scratching his head as to why his strategy backfired against a well-organised Basel side on Wednesday evening.
It looked to be business as usual for Chelsea as they took the lead through Oscar's strike on the stroke of half-time, but they couldn't get the elusive second goal. And it proved costly, with Basel snatching two late goals through Mohamed Salah and Marco Streller to stun the Blues faithful.
Ultimately, it was a poor performance from the Blues from start to finish, with only a few glimpses of dominance in the match. And they never looked dangerous enough to seal the victory, even after going ahead just before half-time.
Tactically speaking, the defeat will come as a surprise mainly because Mourinho didn't choose to alter the setup after Saturday's loss against Everton. Mourinho opted for a more conservative 4-2-3-1 formation, with Samuel Eto'o leading the line once again.
But rather much like the game on Saturday, the 32-year-old looked short of pace and sharpness, and when he did receive the ball, he never looked like doing anything with it. Sure enough, he was getting in the right positions, but the supporters became frustrated with the lack of composure from their centre-forward.
Behind him in the playmaker role was Oscar, with Eden Hazard on the left and Willian making his debut on the right-hand side. With all three players possessing flair and high levels of creativity and movement, the deployment of the trio clicked almost immediately.
Oscar was certainly enjoying the freedom of floating around into pockets of space, receiving short passes from Frank Lampard and Marco van Ginkel. And the link-up with his fellow attacking midfielders looked to be solid, while summer signing Willian looked high on confidence, beating his marker down the right several times and executing brilliant pieces of skill.
For Hazard, it was a difficult first half. Much like the Everton game, when he was on the ball, two defenders rushed to close him down as quick as possible, making it difficult for him to create space or find a teammate.
It appeared that, unlike the rest of the team, there were specific instructions from the Basel manager to keep tight to the 22-year-old and to break up the play when he was on the ball. The Swiss side were happy to sit deep and defend when other players were on the ball, but when Hazard got into his stride, they were quick to limit his influence.
His game was summed up by the lack of help from the referee, who failed to spot several occasions whereby Hazard was felled by his opponents, but was not given a free-kick. What Mourinho needed to do was encourage either one of Ashley Cole or Frank Lampard to support the Belgian winger when he was on the ball, but it didn't happen and he appeared to be rather isolated before the interval.
Part of Mourinho's formation was to have the double-pivot in the centre of midfield which usually consists of Ramires and Frank Lampard. The former tends to operate in a box-to-box role, chasing down opponents and applying pressure in the midfield, while the latter sits deep and controls possession, looking to spread the play out to the wings.
However, with van Ginkel making his debut, the Portuguese coach decided to push Lampard further up the field and have the Dutchman sitting deep, and this was a key decision which simply did not work for Chelsea.
The 20-year-old's first touch was poor at times, and a mistimed tackle as a result saw him booked, which inevitably meant he had to be cautious going into the tackle. Lampard, on the other hand, was successful in the more advanced role, providing the assist for Oscar's goal, but by his standards, it was a quiet night.
Chelsea's main problem was that they lacked fluidity and cohesion in their play, and that was partly due to Basel's excellent defensive setup. David Luiz tried to break the mould by making a few runs further into the opposition's half, and this was the only time where Basel looked vulnerable as they attempted to close down the Brazilian.
Other than that, their movement was static, almost non-existant at times. Mourinho could be heard from the touchline shouting "Pass, pass, pass!" which suggested he wanted his side to play with a higher tempo, like in the first half against Everton. But despite attempts to get the passing style going, it never quite happened for Chelsea.
Again, Mourinho's choice of his defensive partnership was strange, considering the opposition. The pairing of David Luiz and Gary Cahill looked rigid and vulnerable, especially when one of the two chased a ball out of defence. Time and time again, Basel got in behind the two centre-backs, and only Murat Yakin can tell you how Basel didn't score more than twice.
The full-backs—Ashley Cole and Branislav Ivanovic—struggled to get forward, especially Cole, who was pinned back the lively Egyptian Salah. And in terms of their defensive duties, the pair were caught out on various occasions, with Cole guilty of leaving his marker at the back post as he tucked in to aid the centre-backs.
Having just witnessed his side concede, Mourinho responded by bringing off Willian in favour of Juan Mata, but the Spaniard hardly had the chance to make an impact, again looking weeks short of full fitness. The playmaker moved into the middle, rotating with Oscar, who switched to the right, but never found his confidence, although the 25-year-old was always looking to thread through the killer pass.
When the Blues conceded again, Mourinho changed shape, with Lampard and van Ginkel subsequently replaced by John Obi Mikel and Demba Ba. The Blues coach enforced a more attacking 4-1-3-2, with Mikel the holding man. However, neither made the desired impact, and Chelsea were forced to accept defeat once the final whistle went.
All in all, it was a poor performance from Chelsea. Basel came with a plan to defend deep and attack on the break. They frustrated the Blues, and Mourinho may recognise that a change of tactical emphasis will be required if they are to win against Fulham on Saturday.