- Barcelona 5-1 Panathinaikos: As it happened
Panathinaikos took the lead against the run of play through Sidney Govou in the 20th minute but Barca hit back in merciless fashion to take a 3-1 lead by half-time through two goals from the irrepressible Messi and another from David Villa.
Messi, having also hit the crossbar in the first half, spurned the chance to net his hat-trick in the 55th minute when his weak penalty was saved by Alexandros Tzorvas.
However, Messi recovered from that disappointment and set up two more goals for Pep Guardiola's side late on.
For the fourth, Pedro Rodriguez slotted in after the unlucky Messi had seen his shot strike both posts before falling perfectly to the Spain international.
Then, with the last action of the match, Dani Alves headed in Messi's magnificent scooped pass over the Greek side's overwhelmed defence.
Barca came into their Group D opener with twin goals. First and foremost they wanted to make a winning start to a European campaign they hope will end up with a successful and nostalgic return to Wembley stadium next May.
The Catalan giants won the first of their three European Cup crowns at the old Wembley stadium in 1992.
Barca's second reason for wanting to put on a good show tonight was to make amends to their supporters for Saturday's shock 2-0 home defeat to promoted Hercules in La Liga.
Pep Guardiola's side wasted little time in putting Pana under the cosh.
During an opening 12 minutes of almost non-stop Barca attacking the home side went close three times, with Tzorvas superbly parrying efforts from Messi and Xavi before denying Messi a second time.
Incredibly though, it was the Greek visitors who managed to take the lead with what was their pretty much their first venture into Barca's half.
A long punt forward from Tzorvas was cleverly flicked on by Djibril Cisse and Govou outpaced fellow Frenchman Eric Abidal before neatly finishing past Victor Valdes.
That would have come as a huge shock to the 2009 European champions, but they needed just two minutes to get back on level terms and another 10 to take go in front.
The equaliser came when Xavi picked out Messi's run into the area the Argentinian magician coolly side-footed the ball past Tzorvas.
Summer signing Villa then made it 2-1.
Pana defender Stergos Marinos needlessly gave away a corner when he headed the ball virtually out of his goalkeeper's hands, and from the resulting flag kick, Xavi's cross was flicked on by Sergio Busquets and Villa slammed home a half-volley at the far post.
Barca should have been celebrating a 3-1 lead in the 43rd minute but Messi contrived to hit the underside of the crossbar from 10 yards out, but the two-time reigning Spanish champions did not have to wait much longer to celebrate another goal following a magnificent move.
The visiting defence was torn to shreds as Messi played quickfire one-twos with Xavi and Pedro Rodriguez before charging into the area and drilling a low shot past Tzorvas.
The second half merely seemed a question of home many more goals Barca would chalk up.
Messi wasted a gilt-edged chance in the 53rd minute when, after winning the penalty himself, he saw his poorly-struck spot-kick easily saved by Tzorvas.
Tzorvas then denied the same player soon after before Pedro missed a good chance of his own to make it 4-1
Pedro made no mistake in the 77th minute, though, after being presented with the simplest of finishes after Messi's low shot from an acute angle had struck both posts.
The brilliant Messi and Alves then combined in injury-time for the Brazilian full-back to head home his side's fifth and complete a comfortable victory for impressive Barca.