A heavily-rotated Liverpool lost their final Europa League group stage game of the year away at Union Saint-Gilloise on Thursday evening.
The Reds had already won the group by beating LASK last month so the result mattered little as Jurgen Klopp's young side fell to a defeat.
A first senior goal for the ever-improving 20-year-old centre-back Jarell Quansah, their 14th different scorer this season, was the only highlight on a testing evening for Klopp's young guns.
Quansah's 40th-minute leveller equalled a club record 34th-successive goal-scoring match, with Manchester United on Sunday standing in the way of a new landmark and Mohamed Salah, Virgil Van Dijk and Alisson Becker all to return after being left at home.
Liverpool's top spot was already secure despite a second defeat but the win took Union into the Europa Conference League play-offs.
The team's average age was just 21.9 years old - Wataru Endo, 30, five years older than the next senior player - with only Ibrahima Konate and Cody Gakpo considered regular starters.
No surprise then the early threat came from the hosts, defeated only once on home soil this season, with Noah Sidiki and Koki Machida both off target.
A rare attack saw Gakpo's balance fail him at the vital moment after chesting down Conor Bradley's crossfield pass inside the area but Liverpool, with six players 20 or under, understandably struggled for rhythm and control.
Caoimhin Kelleher saved well from Mohammed Amoura and Gustaf Nilsson, who outpaced Quansah to a ball played into the right channel - an avenue from which the opener came.
Both Curtis Jones and Endo looked like they may have been fouled before Amoura burst free to score after Kelleher half-saved his initial effort but VAR ruled there was not enough in those challenges or an offside.
Quansah's goal was perfectly executed; the defender killing dead Jones' corner to blast home as compensation for the last-gasp equaliser VAR denied him in the 4-3 defeat to Toulouse last month.
However, Kelleher's positioning was questionable when Cameron Puertas beat him too easily at his right-hand post just before the break as Union retook the lead.
Joe Gomez replaced Konate - both are competing to start against Manchester United on Sunday but Quansah was the best centre-back on show - and Ryan Gravenberch came on for Endo to reduce the average age even further but it did little to change the flow.
When Puertas beat Kelleher again softly, this time down to his left, Klopp had already sent on Darwin Nunez and 18-year-old left-back Calum Scanlon before VAR ruled out the goal for Lazare Amani's handball.
Nilsson heading wide and Puertas forcing another save maintained the pressure, however, and the fact Liverpool's second shot of the game - Anthony Moris saving from Gravenberch and later from Harvey Elliott - in the 78th minute showed how little impact the visitors had.
