Messi scored his first goal after just five minutes as the Spanish and European champions rebounded from two successive draws to deliver the perfect response yesterday to critics who claimed they had become complacent with success.
Cesc Fabregas, playing in attack with Pedro Rodriguez rested, soon scored their second before David Villa rounded the keeper just after the half hour mark and slotted home.
An own-goal from Ruben Gonzalez added to Osasuna''s misery and Messi was on target again before the break.
There was no drop in pace this time from Barca as in their games against Real Sociedad and AC Milan, and they continued to punish Osasuna.
Xavi lobbed the keeper and then Villa and Messi both struck again to wrap up the scoring.
It will be a warning to Real Madrid who face Levante today that they will not let go of their league title without a fight.
Barca coach Pep Guardiola denied there was ever a problem inside the dressing room and that he was never worried by the criticism.
"I wasn''t angry, people said I was angry but it wasn''t the case. Obviously there is a part of the media which wants Barcelona to do badly and likewise there is a section which wants Real Madrid to do so," he said.
"I am not angry because my players haven''t given me a reason to
be. I defend my players and my job is to convince them that they
can win every game. If one day I think my players haven''t worked
hard enough I will say it."
A Frederic Kanoute goal after half-time gave Sevilla a 1-0 win over Real Sociedad in Saturday''s late game.
The Andalusian side dominated but found it difficult to break down a determined Sociedad.
Alvaro Negredo and Jesus Navas both went close in the first half but it wasn''t until the 53rd minute they finally made the breakthrough with Kanoute firing in a knock down from Negredo.
A poacher''s goal from in-form Roberto Soldado gave Valencia a 1-0 win over Sporting Gijon to maintain their 100 per cent start to the season.
Sporting, who are still to pick up a point, started strongly with plenty of possession but it was Valencia who took the lead through Soldado who has now scored five of Valencia''s six goals so far.
Sloppy defending from the home defence gave Jonas Goncalves plenty of time to shoot but while the keeper Juan Pablo saved well, Soldado pounced on the rebound.
Sporting showed spirit but it was Valencia who looked more dangerous in front of goal.
Soldado could have had a second after the break and substitute Aritz Aduriz also had a shot blocked well by the keeper.
"The game showed the personality of the team and it was a group performance. This was a difficult game against a side which is battling to pick up points so we can congratulate ourselves for the way we played and worked hard," said Valencia coach Unai Emery.
A deflected Martin Demichelis header, which came off Pablo Caceres, gave Malaga a deserved 1-0 victory against Mallorca and Granada picked up their first points of the season with Ikechuwku Uche scoring in a 1-0 victory over Villarreal.