Barca was comprehensively beaten 3-0 by Bayern Munich on matchday one and this was every bit as humiliating as the Catalans lost back-to-back group games in a single season for the first time since 2000-2001.
A nightmare start quickly gave them an uphill battle as Darwin Nunez put Benfica ahead in the third minute, and although Barca was soon dominating, they were extremely wasteful in front of goal.
Marc-Andre ter Stegen got away with a dreadful error early in the second half but Benfica held firm at the back and eventually seized its opportunity to finish Barca off through Rafa Silva and a late Nunez penalty before Eric Garcia saw red to cap a dreadful night for Koeman.
Garcia offered little resistance as Nunez earned Benfica an early lead, the Uruguayan producing a couple of stepovers before finding the bottom-left corner.
Barca quickly began to dominate in response, but a fantastic Lucas Verissimo block prevented Luuk de Jong from finding an empty net.
Frenkie de Jong was similarly wasteful when prodding a low cross wide from close range, and Pedri – a surprise starter so soon after injury – shot agonisingly past the left-hand post a little later.
Ter Stegen summed up Barca's poor decision-making early in the second half, bizarrely opting to rush out in an attempt to cut out a throughball and was beaten to it, but Nunez could only hit the post.
Luuk de Jong then somehow hit the upright from point-blank range at the other end, though an offside call against Ronald Araujo in the lead up spared his blushes somewhat.
Either way, Barca was made to rue its profligacy.
Silva slammed home from 10 yards after Ter Stegen parried a shot right to him and Nunez made it 3-0 with a cool penalty after Sergino Dest handled, with Garcia's late red card for a cynical tug compounding Barca's embarrassment.
Benfica 3-0 Barcelona
● This is the first time that FC Barcelona have lost and have not scored any goal in their first two games in a season in the European Cup/UEFA Champions League.
● FC Barcelona are winless in their last five UEFA Champions League matches (D1 L4), their second worst run in the competition, surpassed only by one of eight games between November 1994 and November 1997 (D3 L5).
● FC Barcelona have not lost in back-to-back games in the group stage in a same UEFA Champions League season since 2000/01 (vs. Besiktas and Milan), the last in which they were eliminated.
● Barcelona have lost in three group stage games in Champions League for first time and with the same result (3-0; against Juventus in 2020/21 and against Bayern Münich and Benfica in 2021/22).
● Barcelona have conceded six goals in two games this season in the Champions League, more than those received in the whole group stage of the previous season (5).
● This has been the first defeat for FC Barcelona against a Portuguese team in Champions League (12 games, W9 D2 L1).
● Benfica have needed five games to score their first goal for Barcelona in UEFA Champions League. Darwin Núñez's goal at 2' 13'' was the second-fastest goal for the Portuguese team in the competition after another by Nico Gaitán against Galatasaray in October 2015 (1' 12'').
● Also, Barcelona have conceded their fastest away goal in Champions League since December 2009 against Dynamo Kiev, when Milevskiy scored at 1' 18’’ from the start.
● Frenkie de Jong has played his 100th game for Barcelona in all competitions, becoming the 11th Netherlands player to reach that figure.
● Memphis Depay has 173 possession lost in his eight games with FC Barcelona in all competitions, more than any other LaLiga player