Sexton converted to make the score 22-5 to Leinster but Scott Spedding raced clear in the 76th minute to reduce Brive's deficit, Agulla again missing the conversion.
Former winner Charlie Spedding joins John Inverdale for Radio Five Live's coverage of the Flora London Marathon between 0830 and 1215, with commentary on the elite races from John Rawling, Mike Costello and Chicago Marathon winner Marion Sutton.