LISBON, Feb 26 (Reuters) - Porto stretched their lead at the top of the Portuguese Premier League to seven points on Sunday when they crushed Beira Mar 5-0.The reigning champions, who drew 1-1 with Chelsea in their Champions League first knockout round, first leg tie on Wednesday, lead the standings on 46 points from 19 matches. Benfica, who host Pacos Ferreira on Monday, have 39. Sporting's hopes of mounting a title challenge suffered a knock when they were held 0-0 at home by bottom club Desportivo das Aves. They also have 39 points. Argentine striker Lisandro Lopez put Porto in front after 17 minutes with a header following a free kick. His compatriot Lucho Gonzalez doubled the lead after 71 minutes and midfielder Raul Meireles made it three with an unstoppable shot. Substitute Alan grabbed the fourth and Brazilian substitute Adriano wrapped up the scoring two minutes from time with a penalty.