Arsenal and Barcelona each got a taste of their own medicine on Wednesday but it was the Londoners who recovered from what looked a terminal condition to register a remarkable 2-1 comeback win in the Champions League last-16 first leg.

The obituaries had been written all around the Emirates Press box as Barcelona handed the hosts, the best passing team in England, a lesson in how it really should be done.

Statistics in football can be misleading, as Wednesday's result clearly showed, but Barcelona's total of 629 passes was more than double their opponents, with Xavi stroking 109 on his own at an 88 per cent completion rate.

As the ball fizzed mesmerically around the perfect playing surface, Arsenal's players were left chasing shadows and their fans were bemused.

"Isn't that what we do to other teams?," they were thinking as the likes of Samir Nasri, Cesc Fabregas and Jack Wilshere battled for a toe-hold against a midfield of World Cup winners.

Amid the myriad quick-fire exchanges there were deadly through balls, one of which by Lionel Messi sent David Villa through for the opening goal after 26 minutes.

Barca could have had more but, just as last year when they allowed a 2-0 lead to slip to a 2-2 draw in the first leg of the teams' quarter-final meeting, they gradually lost momentum and the passes became more lateral.

Arsenal manager Arsene Wenger had been expecting just that pattern in the last-16 first-leg match.

"We had prepared mentally to live with that domination. Usually we have the ball more than our opponent but we were prepared for them to have it 60 per cent tonight," he said.

"We were exposed many times by their possession but we stayed strong and I hoped they would drop off.

"Then we had to take the gamble, we needed to score two goals, but it could have backfired," he added.

Wenger sent on Andrei Arshavin for Alex Song after 68 minutes and Nicklas Bendtner for Theo Walcott but the game still looked to be heading only one way.

Robin van Persie changed everything, however, when, from a position of little obvious danger, he lashed in the 78th-minute equaliser through the tiniest gap at Victor Valdes's near-post.

Barcelona, unfazed, continued to press but five minutes later Arsenal broke from their own box. A terrific ball by Fabregas sent Nasri free down the right and Arshavin arrived to sweep in his pull-back and turn the game on its head.

"I'm very proud for Arsenal tonight because everybody urged us to play differently to our nature," Wenger said.

"We can be proud of the result but more than pride it can strengthen the belief in our philosophy.

"It was a special night and absolutely fulfilled the promise of two attacking football teams. We are a young team, we averaged 23 tonight, and this will give them a special lift," he added.

A year ago Arsenal travelled to the Nou Camp on the back of their 2-2 home draw and took the lead before four goals by Messi sent the Spaniards through 6-3 on aggregate.

Buoyed by the way they absorbed the best they had to offer on Wednesday before handing them a rare defeat, Wenger said they will travel this time with even greater belief.

"I still believe they are the best team in the world but we know we can beat them -- we didn't know that last year," he said.

"We will take encouragement from tonight, be faithful to ourselves in Barcelona and try to score goals," he added.

Barca coach Pep Guardiola was rendered almost speechless by the turnaround.

"How to analyse that? In the end that result isn't too bad but we dominated the game really," he said.

"We created a lot of chances so I'm happy with the performance, we just needed to convert them.

"It was like last year, we started well, but in Europe you play good teams. Arsenal have been playing well in Europe and they always compete well so you have to congratulate them.

"But I'm confident about the return leg. My guys have shown their quality before over the years," he added.

AS Roma coach Claudio Ranieri was left to fight off loud boos and speculation his days at the club are numbered after an embarrassing 3-2 home defeat by Champions League knockout round debutants Shakhtar Donetsk on Wednesday.

Three Serie A games without a win and the club being up for sale had already set tongues wagging that Ranieri's future at Roma was in jeopardy, and the uninspiring display in the last-16 first leg has only raised the pressure.

Flatly asked if he would resign after the multiple defeats, Ranieri responded with a dry: "No, I'm not even thinking of it."

He put on a brave face over his side's performance, denying last season's Italian runners-up were in serious trouble.

"We're not in a crisis, I didn't see a team in crisis today," he said at a news conference where he faced testy questions from reporters.

"A little bit of fragility maybe yes, we shouldn't have reacted in the impetuous manner we did when we were at 1-1," he added.

He was referring to the Giallorossi giving up three goals to the Ukrainians in quick succession that left them two down before halftime and unable to ever regain the momentum despite a superb strike by Jeremy Menez after the break.

Roma took the lead in the 28th minute when midfielder Simone Perrotta headed in a cross from Rodrigo Taddei off Razvan Rat, but fans had little time to savour the goal as Shakhtar equalised a minute later through Jadson's fortunate deflection.

The Ukrainians, who looked fresh despite not having played a competitive match in more than two months, then seized control of the match with a lovely curling shot from just outside the area by Douglas Costa on 36 minutes.