Liverpool's players were subjected to fireworks let off outside their Istanbul hotel designed to disturb their sleep - but it is a second successive loss that must act as the real wake-up call.

The Premier League champions hardly need to go into panic mode as they sit top of the table, but the warning signs of frailty that have dogged the early weeks of their campaign were on display again as they lost 1-0 to Galatasaray in the Champions League.

After a seamless transition following his succession to Jurgen Klopp, the title won so impressively in his first term in charge, head coach Arne Slot has hit the first real bumps in the road.

On current evidence, after spending close to £450m in the summer, this may yet turn out to be Slot's transitional campaign, rather than the smooth takeover from Klopp without any major acquisitions that followed his arrival from Feyenoord.

Alexander Isak, a substitute in Turkey, is still way short of full match fitness following his drawn-out and acrimonious British record £125m move from Newcastle United.

And Florian Wirtz, a little cheaper at £116m from Bayer Leverkusen, currently looks somewhat lost and lightweight while he adjusts to the pace of life at Liverpool.

But this was not a good night for Slot either.

The Dutchman's golden touch with his decision-making deserted him here in Istanbul, the choice to leave Mohamed Salah on the bench backfiring. When the Egyptian was introduced just after the hour, Galatasaray held the lead and the initiative with Liverpool struggling to create chances.

The last time Salah was placed on the bench for a Champions League game was against Rangers in October 2022. You suspect Slot may not do it again in a hurry.

Liverpool, as they were when beaten at Crystal Palace and as they have been all season, were once again exposed by a Galatasaray side that had clearly done their homework well under coach Okan Buruk.

The warning signals were posted in the opening moments when Baris Alper Yilmaz did what other players have done too often for Slot's liking. The forward ran through on goal unchallenged, only for keeper Alisson to rescue Liverpool once more.

Slot used new right-back Jeremie Frimpong as a right-sided attacker, not exactly an act of faith in his defensive abilities, with recognised midfielder Dominik Szoboszlai moved to defence.

It was Szoboszlai who conceded the decisive 16th-minute penalty when he was adjudged to have fouled Yilmaz, Victor Osimhen completing the formalities amid scenes of near hysteria.

As former Scotland winger Pat Nevin so aptly put it on BBC Radio 5 Live: "It is so un-Liverpool."

After the loss at Selhurst Park, the trip to Istanbul was arguably the last thing Liverpool needed, walking into this hostile, fanatical atmosphere that is a ready-built stage for sporting theatre.

Galatasaray's fans gathered in their thousands in the bars and cafes close to this magnificent arena, built on a hill so it overlooks Istanbul, hours before kick-off.

And the cacophony inside also started hours before the start and, when the action began, every Liverpool touch was greeted with deafening, piercing whistles.

To add to Liverpool's misery on this miserable night in Turkey, the outstanding keeper Alisson went off injured in the 56th minute after another save from Osimhen, while in-form striker Hugo Ekitike also limped off later.

One of the major sources of concern in Liverpool's season so far is the lack of impact from Wirtz.

Here is a player clearly rich in talent and pedigree, who attracted strong interest from Manchester City before choosing Liverpool.

He was the Bundesliga's golden boy after his development under Xabi Alonso at Bayer Leverkusen.

Wirtz is playing in a withdrawn role behind Liverpool's striker - Ekitike in Istanbul - but apart from one shot in the first half that forced a save from Galatasaray keeper Ugurcan Cakir, he was once more peripheral. It left him still seeking his first Liverpool goal.

Even the best players sometimes need to bed in, with Wirtz getting to know his team-mates and his team-mates getting to know him, but Liverpool will hope for a spark of inspiration for their £116m man sooner rather than later.

"You're thinking to yourself 'what is the plan? What is the plan to change it massively?" said Nevin, speaking about Wirtz's role.

"Because you didn't need to change much, because it was pretty good before."

And we return to the subject of Slot's transition, from a Liverpool team that was virtually untouched from when he was appointed to winning the Premier League at a canter, to one trying to integrate a host of new players.

The introduction of Wirtz has seemingly resulted in Liverpool being exposed more, although this is not just the German's responsibility. They do not look as secure as they did last season and team shape appears to have been affected.

"I don't see where Wirtz gets into the team," ex-England captain Wayne Rooney said on The Wayne Rooney Show. "I think it was a lot of money. I think Wirtz actually damages the balance of Liverpool and how they play.

"He's a top player and I'm sure he will get better - but he's had a slow start and I think there's no denying that."

Wirtz's current struggles are not down to a shortage of endeavour. He attempted more dribbles or shots on goal than anyone else for Liverpool in Istanbul. He will hope his hard work is rewarded soon.

Liverpool statistics also back up the theory they are now easier to get at, needing late goals against Bournemouth, Newcastle , Arsenal, Burnley, Atletico Madrid in the Champions League and Southampton in the Carabao Cup. They also conceded two-goal leads against Bournemouth, Newcastle and Atletico.

And, again, you can compare the start of this season to the beginning of last - they have had only two clean sheets in 10 games this season having kept six in their first 10 last season.

"Right now they're not there yet," said ex-Liverpool forward Daniel Sturridge on Amazon Prime. "When you look at the way they're playing right now they're not the same team as last year. You can see the chemistry is not right at this present moment in this time - but they have plenty of time to get it right. It's not panic stations."

Slot, perfectly understandably, delivered measured perspective as he said: "We are not so far off the level shown last season. This is sometimes what the schedule can bring, Galatasaray is not a simple game. We now play Chelsea away, a difficult game.

"The margins are small and they were last season. For the second time in a row we are on the wrong side.

"I saw a lot of things in the first half, but the second half was much less. I don't think in the second half there was a lot of playing time, their striker was on the floor four or five times. It was difficult to get momentum in the game."

For all that, however, the sense of calm control and composure that was the hallmark of Liverpool's title win has been lost - and was missing again the fierce surroundings of Istanbul.