Had Sporting failed to win Saturday's Primeira Liga encounter, their city rivals could have celebrated a first league title since 2010 by taking just a point from their home game against bottom-placed Olhanense on Sunday.
However, Adrien Silva scored from the penalty spot in the 52nd minute and, although Marcos Rojo was dismissed for the visitors in the closing stages, Sporting racked up a sixth straight league win.
It appears to be a case of too little too late for Leonardo Jardim's charges, however, as Benfica can wrap up the title by beating Olhanense.
Elsewhere, Pacos de Ferreira suffered a blow in their relegation battle after being thumped 5-0 at home to Nacional.
Miguel Rodrigues put Manuel Machado's men ahead at Estadio da Capital do Movel, in what proved to be the only goal of the first half.
But the floodgates opened after the break, as Mario Rondon and a penalty from Claudemir put the visitors into a 3-0 lead.
Rondon then duly took centre stage by notching two more goals on his way to a hat-trick, before Pacos were further frustrated as Flavio Boaventura received his marching orders in the closing stages.
The result leaves Nacional in fifth place, while Pacos remain in the relegation play-off spot, just two points above bottom place.
Maritimo can no longer overhaul Nacional in fifth, but Pedro Martins' side were 3-1 victors over Academica at Estadio dos Barreiros.
Goals from Derley and Sergio Marakis put the home side 2-0 ahead inside 20 minutes and, although Salvador Agra pulled one back shortly after the break, Fransergio rounded off the win deep into second-half injury time.
Rounding off the action, Estoril's slim UEFA Champions League hopes were dented in a 0-0 draw at Gil Vicente.
