Barcelona showed they were still a favourite to regain the Champions League title after beating a highly-fancied Manchester City side 2-0 in the first leg of their last 16 tie in England.
Billed as the biggest match in City's recent history, it all went wrong for Manuel Pellegrini's side after 53 minutes when defender Martin Demichelis was sent off for a last-man lunge on fellow Argentine Lionel Messi who scored from the resulting penalty to put Barca ahead.
It was the first goal he had scored in an away European tie in England - his goal in the 2011 Champions League final against Manchester United having come at neutral Wembley - and set the Spanish champions on the way to their first win in an away European tie in England for six matches.
Their second goal came in the last minute when Dani Alves collected a pass from substitute Neymar and fired through goalkeeper Joe Hart's legs to give City a difficult task of rescuing the tie in the second leg on March 12.
The referee was not impartial. He did not have any control of the game. I think it was not a good idea to have a referee from Sweden in such an important match.
The defeat sparked an out-of-character attack from Pellegrini who accused Swedish referee Jonas Eriksson of favouring Barca.
The Chilean risks a reprimand and possible severe punishment from football's European governing body UEFA.
"I spoke to him at the end and told him he should be very happy because he decided the match," Pellegrini said.
"Barcelona had no chance to score until the penalty against Demichelis.
"The referee was not impartial. He did not have any control of the game. I think it was not a good idea to have a referee from Sweden in such an important match."
Asked why it was relevant that the referee was Swedish, he replied: "More important football is played in Europe than in Sweden so a big game with two important teams - that kind of game needs a referee with more experience."
Eriksson, a FIFA referee since 2002 who is on the list for this year's World Cup finals in Brazil, has refereed 86 UEFA matches and this was his 22nd Champions League game.
It was also City's first in the knockout rounds of the competition and they rarely showed the kind of form that has brought them 117 goals in all matches this season and prompted talk of a quadruple haul of trophies before this setback.
Barca, with a three-pronged attack of Messi, Andres Iniesta and Alexis Sanchez in front of a typically fluid three-man midfield, dominated the first 20 minutes, allowed City back in the game briefly, then took control again after the dismissal.
'Not so confident'
Their coach Gerardo Martino said he was delighted with the win but was not taking anything for granted for the return.
"I am not so confident yet for the second leg. Our intention was to win and I think it's a fair result.
"But when we allowed City to have the advantage for 10 minutes in the first half and 10 in the second they made it risky for us.
"We have had a good away win and now we have to repeat the performance at home. But City lost at home to Bayern Munich in the group stage and then won away. They are a very dangerous opponent."
In Tuesday's other game, Zlatan Ibrahimovic scored with a stunning strike from outside the penalty area in the highlight of Paris Saint-Germain's imposing 4-0 win at Bayer Leverkusen.
The Sweden striker, who took his tally in this season's competition to 10, also converted a penalty after Blaise Matuidi had given the French side an early lead.
Yohan Cabaye added the fourth two minutes from time and Leverkusen, beaten 5-0 at home by Manchester United in the group stage, had no answer to PSG's slick passing as they slumped to another heavy defeat.