Holders Barcelona and English side Arsenal both saw victory elude them in their opening matches of the Champions League group stages on Tuesday as late goals left them with draws.

A superb second-half freekick by David Villa looked to have secured Barca the three points after they had dominated the match with AC Milan, despite Alexandre Pato's early goal, only for Thiago Silva to head home in the third minute of time added-on to make it 2-2.

Arsenal looked to have secured a much-needed morale boosting win away against German champions Borussia Dortmund until a stunning volley by Ivan Perisic two minutes from time saw the match end in a 1-1 draw.

Arsenal's Premier League rivals Chelsea had no such problems as they won 2-0 against another German side Bayer Leverkusen - for whom Michael Ballack started against one of his former clubs.

Pato showed that the extra rest he'd been permitted by Milan coach Massimiliano Allegri after returning from the Copa America had paid off as he opened the scoring virtually from the kick-off.

The Brazilian - who is engaged to AC Milan owner and Italian Prime Minister Silvio Berlusconi's daughter - broke the Barcelona offside trap to run on and slot the ball past goalkeeper Victor Valdes.

His 24 second strike was the fifth fastest gola in Champions League history.

Barca, though, forced an equaliser late in the second-half as Lionel Messi somehow managed to outstrip two Milan defenders in the box and get in his low cross, which Pedro put away after running in unmarked at the far post.

The hosts, though, suffered a blow in the 39th minute as Andres Iniesta had to go off injured to be replaced by the in-form Cesc Fabregas.

But it didn't stop their domination of the match and Villa's sublime freekick gave them a deserved lead only to be pegged back right at the end.

Arsenal struck just before the break after an evenly fought first-half as van Persie played a neat 1-2 with Theo Walcott and finished it off in style but Dortmund got a deserved draw thanks to Perisic.

Chelsea and Leverkusen both had goals ruled out in the first-half but the London side got on the board in the second-half through David Luiz with a brilliant effort.

Recent Spanish signing Juan Manuel Mata added a second in time added-on.

Chelsea boss Andres Villas-Boas's former side Porto, the club he guided to the Europa League trophy last season, came from behind to beat last season's Champions League quarter-finalists Shakhtar Donetsk 2-1.

Shakhtar, winners of the now defunct UEFA Cup, took an early lead away with Brazilian Luiz Adriano scoring.

Porto, though, fought back and leading striker Hulk levelled before half-time while Pinheiro Kleber stroked in the winner in the second-half.

Marseille have yet to win in the French league this season but they shrugged off that form to win away 1-0 at Olympiakos, a goal by Argentinina star Lucho Gonzalez proving the difference.

Czech Republic side Plzen marked their first appearance in the group stages by taking the lead at home to Belarus outfit BATE Borisov, Marek Bakos scoring in the first-half, but Renan Bressan equalised in the second period to force a 1-1 draw.