Match ends, Paris Saint Germain 4, Barcelona 0.
Angel di Maria scored twice as Paris St-Germain stunned Barcelona to leave the Spanish side in danger of failing to reach the Champions League quarter-finals for the first time in a decade.
PSG dominated this last-16 first-leg tie throughout and took the lead through Di Maria's curled free-kick.
Julian Draxler added a second with an angled drive before Di Maria curled an effort into the top corner.
Edinson Cavani then sealed a famous win with a powerful fourth.
A lacklustre Barcelona - with Lionel Messi, Luis Suarez and Neymar largely anonymous - did not produce an effort of note until seven minutes before the end when Samuel Umtiti headed on to the post.
The defeat leaves Luis Enrique's side with an almighty task to stay in the competition when they host PSG in the return leg on 8 March.
No side has managed to overturn a four-goal first-leg deficit in the Champions League.
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A brutal beating for Barca as Messi goes missing
Barcelona breezed into the knockout stage by topping Group C, winning five of the six games they played.
Their one defeat was also the only time they conceded three goals in a group-stage game, when they lost 3-1 at Manchester City.
At least in that match they managed to score - Messi putting them ahead at Etihad Stadium - but at the Parc des Princes on Tuesday they barely troubled Kevin Trapp in the PSG goal.
The visitors regularly squandered possession and looked lethargic throughout. When they have not been at their best in the past, their star players have stepped up. But on this occasion they offered nothing.
Messi, so often capable of creating something from nothing, made uncharacteristic mistakes and was at fault for PSG's second when he lost the ball to Draxler, who then played a one-two with Marco Verratti to slice through a static defence and put the French side in control.
It was one of the worst Barcelona performances in recent memory but PSG were also at their absolute best and, in truth, could have won by an even bigger margin.
They finished the game with 16 shots on goal, 10 of those on target.
Are PSG serious contenders?
PSG have long been the dominant force in French football, winning their domestic league title every season since 2013, but they are yet to transfer that form into Europe.
They have never progressed beyond the quarter-finals but dominant wins home and away against Chelsea at this stage of the competition last year suggested they had finally joined the continent's elite, only for them to then lose against Manchester City.
Unai Emery, PSG's Spanish manager, had faced Barcelona 23 times before in his coaching career and won just once.
But Emery has form in Europe. He led Sevilla to three successive Europa League titles from 2014, getting the best of the players at his disposal and that is proving to be the case at PSG.
Cavani now has 34 goals in 32 matches while Di Maria is producing consistently what he only managed in flashes at Manchester United. Draxler, who underperformed at Wolfsburg, has excelled since his January move to the French capital.
All three were key to Barcelona's downfall and this could prove to be a watershed moment for both PSG and Emery.
"I think this makes PSG a threat in the competition," former Manchester United defender Rio Ferdinand told BT Sport.
"Mentally they will go on again and they will believe now they are capable of winning this tournament by beating one of the best teams."
Home form hope for Barcelona
Barcelona were one of the favourites to win the Champions League at the start of the season but will now need to produce one of the greatest comebacks in football to stay in the competition.
They are more than capable of scoring goals for fun at the Nou Camp, having hit three or more in six of their previous seven games.
Borussia Monchengladbach were the last side to visit Barcelona in the Champions League and they lost 4-0 in December.
But PSG possess much more quality, with Di Maria and Cavani more than capable of scoring an away goal that would surely put the tie beyond Barcelona.
It is sure to be one of the toughest tests of Enrique's Barcelona career to date.
Man of the match - Angel di Maria
Barca's joint-heaviest defeat - the stats
- Paris St-Germain became the sixth team to score four goals in a Champions League game vs Barcelona (after Milan, Dynamo Kiev, Valencia, Chelsea and Bayern Munich).
- Indeed, this was Barcelona's joint-heaviest defeat in the competition (0-4 vs Milan in 1994, Dynamo Kiev in 1997 and Bayern Munich in 2013).
- Angel di Maria has scored four goals in the Champions League this season - his best return in a single campaign.
- Only Lionel Messi (10) has scored more goals in the Champions League this season than Edinson Cavani (seven).
- No side has ever turned round a 4+ goal deficit to progress in a Champions League knockout tie.
- Barca faced 10 shots on target vs PSG - their joint-highest in a Champions League match since 2003-04 (also vs Bayer Leverkusen in December 2015).
- 6VerrattiSubstituted forNkunkuat 70'minutes
- 25RabiotBooked at 3mins
- 11Di MaríaSubstituted forLucas Mouraat 61'minutes
- 23DraxlerSubstituted forPastoreat 86'minutes
- 7Lucas Moura
- 17Cabelino Andrade
- 21Ben Arfa
- 1ter Stegen
- 21André GomesBooked at 33minsSubstituted forRafinhaat 58'minutesBooked at 74mins
- 5BusquetsBooked at 62mins
- 8IniestaSubstituted forRakiticat 73'minutes
- 6D Suárez
- Szymon Marciniak
- Shots on Target
Second Half ends, Paris Saint Germain 4, Barcelona 0.
Jordi Alba (Barcelona) wins a free kick in the defensive half.
Foul by Lucas Moura (Paris Saint Germain).
Foul by Luis Suárez (Barcelona).
Adrien Rabiot (Paris Saint Germain) wins a free kick in the defensive half.
Corner, Barcelona. Conceded by Thomas Meunier.
Neymar (Barcelona) wins a free kick in the defensive half.
Foul by Christopher Nkunku (Paris Saint Germain).
Attempt missed. Neymar (Barcelona) right footed shot from outside the box is too high from a direct free kick.
Neymar (Barcelona) wins a free kick in the attacking half.
Foul by Adrien Rabiot (Paris Saint Germain).
Foul by Jordi Alba (Barcelona).
Lucas Moura (Paris Saint Germain) wins a free kick on the right wing.
Substitution, Paris Saint Germain. Javier Pastore replaces Julian Draxler.
Attempt missed. Ivan Rakitic (Barcelona) header from the left side of the box is high and wide to the left.
Samuel Umtiti (Barcelona) hits the left post with a header from very close range. Assisted by Gerard Piqué with a headed pass following a corner.
Corner, Barcelona. Conceded by Layvin Kurzawa.
Ivan Rakitic (Barcelona) wins a free kick on the left wing.
Foul by Thomas Meunier (Paris Saint Germain).