Arne Slot's 100th game in charge of Liverpool ended in defeat as Galatasaray established a narrow last-16 Champions League lead to take to Anfield next week.

In front of a hostile home crowd in Istanbul, Liverpool's familiar shortcomings resurfaced as Mario Lemina nodded the seventh-minute winner - the 10th goal Slot's side have conceded from corners this season.

The former Southampton, Fulham and Wolves midfielder was well placed to head past Giorgi Mamardashvili, making a rare start in the absence of injured first-choice goalkeeper Alisson, from close range after Victor Osimhen's headed on a Gabriel Sara set-piece.

It was Lemina's first goal of the season - and five years ago he scored the winner at Liverpool for Fulham in a Premier League game.

Osimhen thought he had made it 2-0 after a calamitous mistake by Ibrahima Konate, but the close-range effort was ruled out after Baris Alper Yilmaz was deemed to be offside in the build-up, even though he didn't touch the ball.

Liverpool thought they had equalised in the 70th minute after the ball was bundled over the line from Dominik Szoboszlai's corner.

But that was also ruled out following a lengthy check after the video assistant referee (VAR) ruled the ball hit Konate's arm twice - firstly from the corner delivery, and then after the ball came off Virgil van Dijk's heel.

"If it's correct that the goal was disallowed, which is difficult to judge as I've heard different opinions from people, it's not completely obvious but let's say that decision is right," said Slot when asked about Liverpool's disallowed goal.

"In the Premier League there is much more allowed than in the Champions League.

"That's why I was so surprised it wasn't a penalty because in all the other incidents where he (the referee) thought he saw something when we made a foul and was so fast to blow his whistle and give Galatasaray a free-kick."

In a frantic match, the Reds should have been ahead before Galatasaray's early breakthrough, but Florian Wirtz fired narrowly wide after an error by home keeper Ugurcan Cakir.

Even after conceding, they had chances to get themselves back on level terms.

Wirtz forced Cakir into a save before Konate drilled agonisingly over the bar, before Mamardashvili rescued the visitors.

The Georgia keeper produced a fine stop to deny former Spurs defender Davinson Sanchez from doubling his side's lead.

But the Turkish champions looked hesitant at the back and Cakir stretched out a left hand to make a stunning save to keep out Hugo Ekitike's chipped finish after a good run by the French forward.

Liverpool thought they had equalised in a goalmouth scramble, only for VAR to intervene and leave Slot's side with it all to do in the second leg at Anfield on 18 March.

Liverpool's vulnerability from corners has been a thorny issue all season - and so it proved again in Turkey. Only West Ham (15), Chelsea (12) and Nottingham Forest (12) have let in more among Premier League sides.

The goal that decided the first leg came after Osimhen was allowed to rise unchallenged to meet Sara's corner, and the Nigeria forward headed it straight to Lemina to finish on a bitterly frustrating night for the visitors.

While Istanbul may evoke memories of celebration for Liverpool fans after their extraordinary comeback win over AC Milan in the 2005 final, the Reds have now failed to win in four away games against Galatasaray.

Having lost 1-0 to the Turkish champions in the league phase back in September, this was a test to see if Slot's side had learned lessons.

The answer soon became apparent when they conceded early, while there was huge relief when Osimhen's goal - which would have been his eighth in this season's competition - was ruled out after Konate got his feet in a tangle.

A 2-0 deficit would have left Liverpool facing an enormous task in the return, yet they are still going to have to come from behind to reach the quarter-finals.

Failure to get through - just as they did last season with a last-16 exit against Paris St-Germain - will only increase the pressure on Slot's position.

The Reds next host Tottenham in the Premier League on Sunday, 15 March (16:30 GMT) before the return leg with Galatasaray at Anfield on Wednesday, 18 March (20:00).

Watch highlights of every Champions League game from 22:00 on Wednesday on BBC iPlayer and the BBC Sport website and app.

There will also be a Champions League Match of the Day on BBC One on Wednesday, from 22:40 to 00:00.