Benfica failed to score for the first time in 93 home games on Sunday, drawing 0-0 with FC Porto in the Portuguese league.
Benfica leads Porto by three points at the top of the standings with four games to play.
The defences prevailed at the Stadium of the Light despite the match having the league's top three scorers — Porto's Jackson Martinez with 17 goals and Benfica's Brazilian duo of Jonas (16) and Lima (14).
Benfica won at Porto 2-0 earlier this season, meaning the defending champions prevail if they finish level on points.
Benfica is pursuing its first back-to-back titles in 31 years.
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