Barcelona striker Robert Lewandowski scored a hat-trick in the second half to help his side fight back to claim a hard-fought 4-2 win on Monday over visitors Valencia, who were leading 2-1 when they were reduced to 10 men just before the break.With five games remaining, Barca moved back to second in La Liga on 73 points as they leapfrogged surprise package Girona, who are third with 71. Those two teams will meet in a Catalonia derby on Saturday which could decide a top-two La Liga finish and a place in the Spanish Super Cup.Barcelona’s win postponed for a couple of weeks Real Madrid’s almost inevitable La Liga title celebrations as Carlo Ancelotti’s side sit atop the standings on 84 points. Valencia stay eighth on 47 points, two points behind Real Betis and four off Real Sociedad in the battle for a European qualifying spot.In Barca’s first game since boss Xavi Hernandez said he was reversing his decision to step down at the end of the season, they struggled on a wet surface after heavy rain turned the match into a frantic tussle marked by goalkeeping mistakes. The visitors wasted a sitter from close-range through Peter Federico early and then allowed Fermin Lopez to head home from a Raphinha cross to put Barca in front after 22 minutes.But Valencia’s Hugo Duro struck in the 27th, taking advantage of an error by keeper Marc-Andre ter Stegen who tried to chip a clearance from the edge of the box but instead gifted the ball for the striker to equalise into the empty net. Another mistake by Barca’s defence 11 minutes later saw Ronald Araujo bundle over Federico and Pepelu converted the penalty to give the visitors the lead.However, Valencia were soon down to 10 men when keeper Giorgi Mamardashvili handled as he raced outside his area just before the break and was shown a red card as the last man. He failed to control a back pass and stopped the ball with his arm to stop Lamine Yamal running through on the empty goal.Barca piled on the pressure after halftime and Valencia crumbled, with Lewandowski scoring with two headers from corners in the 49th and 82nd before netting a free-kick in added time.“It wasn’t easy... In the first half we didn’t have much space,” Poland striker Lewandowski said. “But the important thing is that we are Barca and we know that, although we conceded two goals, we can score three and four goals. “We knew we had to play with patience in the second half. We’re good now and we have to think about Girona.”