Robert Lewandowski scored twice in three minutes as La Liga leaders Barcelona thrashed Real Madrid in El Clasico to move six points clear of their rivals.Real were looking to extend their run of unbeaten games to 43 in the league, which would have equalled the record set by Barcelona between April 2017 and May 2018.But their hopes of doing that were quashed by a devastating second-half display by their opponents.After a goalless first half, Lewandowski broke the deadlock in the 54th minute with a clinical finish from Marc Casado's through ball.The Poland striker then stunned the hosts with a second, heading Alejandro Balde's cross into the right corner.Lewandowski had two good chances to complete a hat-trick, hitting the woodwork from the first before firing over from a good position.Spanish teenage star Lamine Yamal, 17, got Barcelona's third when he drove into the top corner from an angle before Raphinha lobbed a fourth late on as both players scored in El Clasico for the first time.The result ensured Kylian Mbappe's first taste of the famous fixture ended in defeat with the France striker having had two goals disallowed for offside and also been denied by Inaki Pena in the Barcelona goal.