Having twice squandered leads during the past week with costly lapses in defense, Barcelona erased any questions about its defensive strength with an overwhelming attacking display that gave Osasuna no chance at Camp Nou stadium.
Barcelona was up 5-0 by halftime through Messi's double, goals by Cesc Fabregas and David Villa, and Osasuna defender Roversio's own goal.
Messi assisted Xavi Hernandez at the beginning of the second half before Villa and the Argentina star capped the win late.
"I think we played very well. It wasn't a perfect game, but we created a lot of scoring chances," Barcelona midfielder Sergio Busquets said. "It's true that we were coming off two draws and nobody was pleased with that. This was an important win." Messi is tied with Valencia's Roberto Soldado as the league's leading scorer with five goals each — one more than Real Madrid's Cristiano Ronaldo.
Elsewhere, Soldado gave first-place Valencia a 1-0 win at Sporting Gijon, and promoted side Granada beat Villarreal 1-0 for its first win in Spain's first division in 35 years.
Malaga edged Mallorca 1-0, and Sevilla downed Real Sociedad 1-0.
Barcelona showed that while its defensive line may be thin, it has a surplus of attacking players as the absence of the injured Andres Iniesta and Alexis Sanchez went unnoticed.
Even so, the European champion looked set to make yet another mistake just two minutes in when Osasuna forward Juan "Nino" Martinez almost surprised goalkeeper Victor Valdes with a cross that hit the crossbar.
But Pep Guardiola's team settled in and quickly went about picking apart its visitors.
Messi finished off another example of Barcelona's exquisite one-touch passing game five minutes in when Dani Alves headed on Busquets pass for the two-time Ballon D'Or winner to tap over the goal line.
Messi and Fabregas demonstrated once again they haven't missed a beat since they played together as teenagers on Barcelona's youth team when Messi lofted a pass to a streaking Fabregas who expertly volleyed it into the right corner of the net to double Barcelona's lead in the 13th.
"Cesc grew up here. He has (Barcelona academy) La Masia in his veins and his legs," Villa said. "Everyone knew that he was going to provide us with the plus he's giving us." Barcelona made sure not to relax after letting leads slip to draw 2-2 against both AC Milan and Real Sociedad in the last week, and soon put the result beyond doubt.
Messi hit the post with a header in the 30th, but four minutes later Villa scored his first goal of the Spanish season.
The Spain striker created Barcelona's fifth when Osasuna goalkeeper Andres Fernandez blocked his strike, only to see it ricochet off Roversio and into the back of his net in the 40th.
A minute later it was Fabregas' turn to draw in the defense before laying off for the unmarked Messi to rifle a shot into the net.
Messi was denied again by the woodwork shortly after halftime, but he soon found Xavi alone to chip over the flatfooted Fernandez.
With Osasuna demoralized, Fabregas set up Villa to get his double in the 76th, and Messi then dribbled through the middle of the defense before slotting in his third three minutes later.
"I'm happy because we wanted to have a lot of players in the middle of the pitch to be able to play more and create scoring chances," Guardiola said. "There are always things you can do better and our goal is to always improve in attack." Last season, Barcelona recorded its biggest away win when it beat Almeria 8-0.
Its most lopsided win ever came in the 1949-50 season when it beat Gimnastic 10-1.
In Gijon, Soldado scored on the half-hour mark to keep Valencia perfect and atop the standings, while Sporting fell into last place.
Meanwhile, Ikechukwu Uche, who is on loan to Granada this season from Villarreal, headed Siquiera's cross past Villarreal goalkeeper Cesar Sanchez in the 56th for the Andalusian team's first goal of the season.
Villarreal had a perfect opportunity to salvage a draw in the 78th but Giuseppe Rossi hit the post from his penalty kick and Jonathan De Guzman fired the rebound wide as the "Yellow Submarine" stayed winless this campaign.
At Iberostar stadium, Martin Demichelis got his team's second straight win with a 39th-minute header off a free kick from Santi Cazorla.
In Seville, forward Frederic Kanoute scored from Alvaro Negredo's pass in the 53rd for Sevilla's second win of the season.
