Robert Lewandowski and Raphinha struck twice each as Barcelona romped to a 5-1 win at Villarreal on Sunday in a wild match to maintain their perfect start to La Liga.

The leaders' sixth straight league triumph was marred by an potentially serious knee injury to goalkeeper Marc-Andre ter Stegen, who was taken off on a stretcher.

"I think it will be a huge injury, when he laid down on the field... you can see it directly," Barcelona coach Hansi Flick told DAZN.

Lewandowski netted Barcelona's first two goals and later missed a penalty in a thoroughly entertaining battle on Spain's east coast at Villarreal's Estadio de la Ceramica.

Ayoze Perez pulled his team back into the game shortly before half-time and the hosts had two goals disallowed, with Pablo Torre and Raphinha's strikes cementing Barcelona's victory.

After second-placed Real Madrid thrashed Espanyol 4-1 on Saturday the Catalans were able to restore a four-point lead on the champions.

"It's very important for us that we played a game away from home, we scored five goals and in the end we have three points," said Lewandowski.

"In the end it doesn't matter how, as long as we win that's perfect."

Flick gave Eric Garcia another start in defensive midfield despite his early red card against Monaco in the Champions League midweek.

The German coach also started reserve team players Gerard Martin and Sergi Dominguez, as well as playmaker Torre in place of the injured Dani Olmo.

Teenage star Lamine Yamal hit the post early on before Lewandowski slotted home in the 20th minute after Torre slipped him in.

Villarreal goalkeeper Diego Conde did well to keep out a bundled effort from the Polish striker but Lewandowski pounced after 35 minutes for his second.

Conde saved Garcia's header well but the former Bayern Munich hitman converted the rebound with an acrobatic finish from close range.

It was his sixth La Liga goal of the season, taking him two clear of Real Madrid's Kylian Mbappe in Spain's golden boot race.

- Frantic clash -

Villarreal were frequently threatening on the counter and Perez gave them a lifeline after the electric Nicolas Pepe set him up.

Ter Stegen thwarted Pepe with a sensational save one-on-one before half-time but the German was soon stricken as he fell badly after catching a corner before the break and was replaced by Inaki Pena.

Pepe finished brilliantly early in the second half but his effort was disallowed for a marginal offside call, and Yeremy Pino hit the bar with a header as Marcelino Garcia Toral's side drove Barcelona back.

Torre extended Barca's lead with a deflected strike from the edge of the box, a killer blow given Villarreal's momentum.

Lewandowski hit the post from the spot after Eric Bailly scythed down Yamal and Villarreal's Thierno Barry had a goal ruled out for offside.

Raphinha ended any hopes of a home comeback, first with a deflected shot and then finishing after a superb Yamal pass left him with just Conde to beat.

Despite the emphatic victory and 100 percent start, if Ter Stegen's injury proves to be severe it could dent Barcelona's title hopes.