LISBON, Jan 26 (Reuters) - Benfica moved to within eight points of Portuguese league leaders Porto with a 3-1 away win over Vitoria Guimaraes on Saturday.The match was marred by skirmishes involving rival fans, resulting in at least three injuries, one man being stabbed in the chest, police said. Porto can restore their 11-point advantage at the top of the table after 17 matches with victory at Sporting on Sunday. Paraguay striker Oscar Cardozo put Benfica in front with a superb 30-metre free kick after just eight minutes. Benfica, who had dropped points in their previous two games, doubled their lead when Uruguayan Maxi Pereira tapped in from close range after 26 minutes. Guimaraes pulled a goal back after 60 minutes when French midfielder Kamel Ghilas headed home a free kick by his compatriot Yves Desmarets. But Cardozo pounced on an error to ram home Benfica's third goal in injury time to inflict a first home league defeat of the season on third-placed Guimaraes. Before kickoff, the Benfica players placed flowers on the spot where Hungarian teammate Miklos Feher collapsed and died during a league game with Guimaraes in January 2004.