MADRID: Robert Lewandowski and Raphinha struck twice each as leaders Barcelona maintained their perfect start in La Liga by romping to a 5-1 win at Villarreal on Sunday but were left fearing a season-ending knee injury to goalkeeper Marc-Andre ter Stegen. Atletico Madrid, fourth, were held to a 1-1 draw at city rivals Rayo Vallecano as Conor Gallagher netted his second goal for the Rojiblancos. Barcelona’s sixth league triumph in six games as they bounced back from their 2-1 loss against Monaco in the Champions League on Thursday was marred by Ter Stegen being taken off on a stretcher after falling awkwardly having collected a cross. The club said on Monday the 32-year-old Germany international will undergo surgery after suffering a complete rupture of the patella tendon in his right knee, with Ter Stegen potentially sidelined for the rest of the season. Lewandowski netted Barca’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 previously unbeaten 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.” Lewandowski opened the scoring after 20 minutes with a simple first-time finish and added a second in the 35th with an overhead kick from close range after the ball bounced off goalkeeper Diego Conde. Villarreal were far from giving up and Perez pulled a goal back in the 38th minute before brilliant Ter Stegen denied Nicolas Pepe from levelling just before the break but the Barca captain was soon stricken as he fell badly after catching a corner and was replaced by Inaki Pena. Barca, however, yet again proved unstoppable and Torre added a third with a shot from outside the box in the 58th minute before Raphinha netted his fourth and fifth goals of the campaign to seal the win. In a Madrid derby clash Diego Simeone’s unbeaten Atletico could not find a way past Rayo. Rayo’s Isi Palazon slammed home from close range after 35 minutes and the goal was eventually given after initially being ruled offside. However Gallagher finished neatly from the edge of the box early in the second half when Alexander Sorloth fed the England international. “[At half-time Simeone] told us we all had to run, these days anyone who is not running here cannot play,” Atletico captain Koke told Movistar. “We had chances to get the winner but it wasn’t to be.” Athletic Bilbao overtook Atletico to move into third with a 3-1 win against Celta Vigo.