RIO DE JANEIRO, Feb 4 (Reuters) - Flamengo kept their hopes alive of retaining the Brazilian league title with a 2-0 win over city rivals Vasco da Gama at the Maracana stadium on Thursday.Gabriel Barbosa opened the scoring with a penalty on the stroke of halftime before Bruno Henrique doubled their lead with a powerful header after 77 minutes.The result leaves Flamengo two points behind leaders Internacional with four games to play. The two sides meet in the penultimate round of matches on Feb. 21.Vasco sit two points above the relegation zone. (Reporting by Andrew Downie in London; Editing by Peter Rutherford )