Barcelona suffered a 2-1 defeat at Arsenal and AS Roma's miserable run continued with a 3-2 home loss to Shakhtar Donetsk in Champions League last-16 first-round matches on Wednesday.
For once, Lionel Messi's goalscoring instincts deserted him as Barcelona squandered a 1-0 lead when Robin van Persie and Andrei Arshavin struck late to give Arsenal an unlikely edge to take into the second leg at the Nou Camp.
"It was a game between two special teams in my opinion," Arsenal manager Arsene Wenger, whose side were often left chasing shadows in the first half, said.
"We suffered in some spells during the game but never gave up. We have shown special strengths and shown great resilience."
In Rome, Brazilians Jadson, Douglas Costa and Luiz Adriano scored before halftime for Ukrainian side Shakhtar in the Stadio Olimpico in what was the visitors' first appearance in the competition's last 16 and their first competitive match since early December.
Simone Perrotta had given Roma the lead but the Italians needed a 61st-minute effort from Jeremy Menez to give themselves some hope for a daunting trip to Ukraine.
Roma were booed off the pitch at halftime with much of the fans' anger being vented at under-fire manager Claudio Ranieri.
"It was a game decided by episodes," Ranieri told Sky Italia. "We could have crumbled but we reacted, we couldn't have done better than that. We won't give up. In the return leg we can do to them what they have done to us."
Barcelona again produced some scintillating football at The Emirates and will feel hard done by to return home with a rare defeat that sets up an intriguing second leg.
Messi, who scored a hat-trick when Barcelona beat Arsenal 4-1 to wrap up a 6-3 aggregate victory in last season's quarter-finals, set up David Villa to put the Catalans ahead after 26 minutes.
But the Argentine wasted two gilt-edged chances to add to Barcelona's tally and had a goal disallowed before Arsenal rode their luck to garnish a superb game with some Barca-type football of their own.
Van Persie equalised with a shot from an acute angle after 78 minutes and substitute Arshavin finished off a sweeping move seven minutes from time.
Barca coach Pep Guardiola, whose side's record 16-match winning sequence in La Liga was ended in a 1-1 draw with Sporting Gijon on Saturday, was not too troubled by defeat.
"I think we more or less controlled the game and we just need to create the chances we did tonight in the Nou Camp and then take them," he said.
"It will be an open game I am sure. Yes we have lost tonight, but we still have the second leg."
Arsenal's north London neighbours Tottenham Hotspur won 1-0 at AC Milan and Valencia drew 1-1 with Schalke 04 in Tuesday's matches. The remaining four first-leg games are next week.