An incredible 18 goals were scored across four European matches involving Premier League clubs on a night of drama, as Liverpool and West Ham United came from behind to win, while Brighton & Hove Albion and Aston Villa were edged out in five-goal thrillers.
Second-half goals from Darwin Nunez, Luis Diaz and Mohamed Salah ensured comeback kings Liverpool marked their first UEFA Europa League match since the 2016 final with a 3-1 victory against LASK.
How the match unfolded
Jurgen Klopp made 11 changes to the starting XI that beat Wolverhampton Wanderers last weekend, and for the fourth time in five matches, his side fought back to claim victory.
In doing so, Klopp became the first manager in the club's history to reach 50 wins in Europe.
The boss making Reds history tonight ❤️ pic.twitter.com/A3uNmA1RvS
— Liverpool FC (@LFC) September 21, 2023
In a stuttering first-half display the volume of those changes was clearly felt with Florian Flecker's superb strike from the edge of the area giving LASK a 19th-minute lead.
Nunez fired Liverpool level from the penalty spot on 56 minutes after a foul by defender Philipp Ziereis on Diaz, before the latter lashed home a second from Ryan Gravenberch's cross seven minutes later.
However, Gravenberch limped off with a knock 15 minutes from time and was replaced by Salah, who put Liverpool 3-1 up in the closing stages with a cool finish through goalkeeper Tobias Lawal's legs.
Liverpool will be looking to continue their unbeaten start to the 2023/24 season on Sunday when they host West Ham at Anfield.
See: Liverpool report and line-up
James Ward-Prowse continued his sparkling start at West Ham with two assists to inspire a 3-1 UEFA Europa League win against Backa Topola at London Stadium.
How the match unfolded
West Ham racked up seven corners in a dominant first-half display against the Serbian champions, who were playing in Europe for the first time in their 110-year history.
Mohammed Kudus nearly marked his full Hammers debut with a goal, but his effort deflected narrowly wide of the upright before fellow debutant Konstantinos Mavropanos headed inches off target.
Backa Topola stunned the London Stadium crowd two minutes into the second half when Angelo Ogbonna lost possession on the halfway line and Petar Stanic sprinted forward before placing the ball past Lukasz Fabianski.
Back came West Ham, and two goals in four minutes turned the match on its head.
Said Benrahma's wicked cross was turned into his own net by Nemanja Petrovic on 66 minutes before Ward-Prowse took centre stage.
The former Southampton midfielder, who had either scored or assisted in all four of his West Ham appearances prior to Thursday night's match, whipped over a great corner for Kudus to nod West Ham 2-1 ahead after 70 minutes.
Ward-Prowse then laid on a third and final goal with another perfect delivery that Tomas Soucek powered home for his first goal of the season.
West Ham will look to continue their positive start to the season in Sunday's trip to Anfield.
See: West Ham report and line-up
Battling Brighton's first ever foray into European football ended in disappointment as AEK Athens grabbed a heartbreaking late winner to claim a 3-2 UEFA Europa League success.
How the match unfolded
Key defender Lewis Dunk was ruled out through injury and the Seagulls struggled without their captain's organisational qualities at the back.
Igor Julio and Ansu Fati came in to make their full debuts on a historic night that also saw James Milner become the first player to play in European competition for five different clubs - Newcastle United, Manchester City, Liverpool, Villa and Brighton.
Djibril Sidibe and Mijat Gacinovic took advantage of Dunk's absence to score from set-pieces either side of Joao Pedro's 30th-minute penalty.
A sold-out Amex Stadium produced an incredible atmosphere and Seagulls fans raised the roof when they were awarded a second penalty on 66 minutes following a VAR review.
Pedro sent Cican Stankovic the wrong way from the spot for a second time to level at 2-2 and the momentum was with Brighton.
This guy knows how to take a penalty. 🥶 pic.twitter.com/NcFeKeskqd
— Brighton & Hove Albion (@OfficialBHAFC) September 21, 2023
Kaoru Mitoma had an effort blocked and Pedro could have claimed his hat-trick when he was put through on goal by Jan Paul van Hecke, only for Stankovic to block with his legs.
But with six minutes remaining, Tariq Lamptey slipped as AEK launched a speedy counter-attack, and Ezequiel Ponce applied the finishing touch to Niclas Eliasson's cross.
There was still time for Simon Adingra and Pervis Estupinan to go close, but Brighton couldn't find a way through for a third time and will quickly turn their attention back to Premier League action and Sunday's south-coast derby at home to AFC Bournemouth.
See: Brighton report and line-up
The defensive lapses that have plagued Aston Villa this season were on show again as Unai Emery's side were beaten 3-2 in their Europa Conference League group opener at Legia Warsaw.
How the match unfolded
Villa, who have conceded 10 goals from their five Premier League matches so far, went behind after only three minutes when Pawel Wszolek stole in unmarked to slot home.
In a frenetic opening, Villa were back on level terms within three minutes. Nicolo Zaniolo's shot was pushed onto the bar by home 'keeper Kacper Tobiasz only as far as Jhon Duran, who headed past him from close range.
Villa enjoyed a spell of possession, but were picked apart defensively for a second time on 26 minutes, this time Wszolek turning provider for Ernest Muci, who had time to pick his spot.
Lucas Digne's stunning half-volley brought Villa level for a second time seven minutes before the break.
Another piece of sloppy defending cost Emery's side dear after the restart as Muci was given the freedom of the Villa rearguard to fire a superb low shot into the far corner.
Jacob Ramsey spurned a great chance to nick a point on his return from injury, but drove wide before Leon Bailey fired into the side-netting in stoppage time.
Villa will be aiming to get back to winning ways at Chelsea on Sunday, where they are looking to secure back-to-back league victories against the Blues for the first time since October 1993.