World Player of the Year Lionel Messi netted twice and Spain Under-21 midfielder Thiago Alcantara was also on the scoresheet for Barca in their bid for a club record-equalling fourth consecutive Spanish title.
The victory was an impressive response to title rivals Real Madrid after Jose Mourinho's side inflicted a 6-0 demolition on Real Zaragoza on Sunday when Portuguese forward Cristiano Ronaldo scored a hat-trick.
With 75,000 fans packed into a sultry Nou Camp, Barca coach Pep Guardiola opted to leave Spanish World Cup winners Xavi and David Villa on the bench and started with Fabregas in midfield alongside Alcantara, Andres Iniesta and Seydou Keita.
With a number of defenders missing, including injured centre-backs Carles Puyol and Gerard Pique and the suspended Daniel Alves, he deployed Sergio Busquets in a three-man defence with Javier Mascherano and Eric Abidal.
After dominating the early stages, Barca went ahead on 25 minutes. As Alcantara ran at the Villarreal defence they backed off waiting for a pass, allowing him space to shoot low past Diego Lopez into the corner of the net.
BIG PERSONALITY
Former Arsenal captain Fabregas, who returned to his boyhood club this month after eight years with the Premier League side, made it 2-0 just before half-time when he raced on to a Messi pass, rounded Lopez and slotted home.
The 24-year-old, who also scored from a Messi assist in Barca's 2-0 European Super Cup win over Porto on Friday, was at the Catalan club's youth academy with the Argentina forward and the pair already look to have created a formidable partnership.
"Cesc knows his team-mates very well," Guardiola said at a news conference. "He has a very big and strong personality. He was the captain of an important team."
Chilean Sanchez, another new signing following his close-season move from Udinese, put Barca three up two minutes after the break before Iniesta played Messi through to round Lopez and make it 4-0 five minutes later.
Messi grabbed a second and Barca's fifth when he turned in Alcantara's fine centre with 15 minutes left.
La Liga kicked off a week late at the weekend after the first round of matches fell victim to a strike called by the players' union (AFE) over unpaid wages. The dispute with the league (LFP) was finally resolved on Thursday.
Villarreal's defeat and a shaky performance on Saturday from Valencia, the other two Spanish teams in this season's Champions League, suggests it will again be a straight fight between Barca and Real for the title.
DOMESTIC DOMINANCE
Villarreal coach Juan Carlos Garrido noted at his post-match news conference that Barca and Real's domestic dominance was due to them being so much richer than their La Liga rivals.
Barca's annual budget was just under 430 million euros last season compared with less than 70 million at Villarreal.
"Today we
