The Greek champions surprisingly opened the scoring, but the Blaugrana were not impressed and cruised to a comfortable win...
David Villa then gave the Catalans the lead after a corner kick before Messi doubled his personal tally minutes before the break. Messi missed a spot kick in the second half, but Pedro did find the net to make it 4-1 for Barca. Brazil international Daniel Alves made things even worse for Pana in stoppage time.
The home side started the match brilliantly and created several chances to open the scoring in the early going. However, Alexandros Tzorvas pulled off an excellent save to deny Messi after his subtle header.
Minutes later, Xavi failed to find the net from five yards out after a fantastic pass from Andres Iniesta. The Spain international had all the time and space he needed to tap home from close range, but Tzorvas again made a good save to keep the match scoreless early on.
The Greek champions then opened the scoring from out of nowhere. Djibril Cisse found Sidney Govou with an intelligent backheel and the former Lyon star found the net on pretty much the first occasion Panathinaikos left their own half.
Barcelona weren't impressed too much though and restored parity within 60 seconds. Xavi set up Messi with a superb through pass and the Argentina star beat Tzorvas with a lobbed attempt. The Spanish giants then grabbed the lead around the hour mark. Sergio Busquets headed a corner in the path of David Villa and the prolific striker had no problems finding the net from close range.
Messi continued to cause the Panathinaikos defence all kinds of trouble and almost doubled his personal tally minutes before the break when he hit the crossbar with a left footed strike. Messi did get his brace minutes later though. The Argentine wizard started a combination with Pedro and calmly fired home after getting the ball back.
The away side continued to focus on defending in the second half and only looked dangerous once or twice when Sebastian Leto got involved. Barca on the other hand got some good opportunities to score a fourth goal, with Messi getting the best chance from the spot in the 57th minute. However, Tzorvas saved his weak shot with ease.
Bojan Krkic then played a delightful through ball for Messi near the byline on the left side of the penalty box. The Argentine let loose from a really tight angle and the ball cannoned off the right post, rebounded off the left post, and fell to Pedro who converted from close range. Daniel Alves poured even more salt in Panathinaikos' wounds with a goal well into stoppage time.
Barcelona sit atop of the table in Group D following the home win. The Catalans travel to Russia in two weeks for the match against Rubin Kazan, while Panathinaikos host Copenhagen on 29 September 29.
Domestically, Barcelona meet Atletico Madrid at the weekend in their third league match of the season while Panathinaikos await an away game against Kavala on Saturday evening.