Third-placed Sporting - six points behind Benfica ahead of the leaders' match with Vitoria Setubal on Sunday - fell behind when Rui Fonte struck in the 69th minute.
Marcos Silva's team seemed destined for defeat when Cedric collected a second yellow card seven minutes from time but Mane slammed home from close range deep into stoppage time.
Earlier on Saturday, Gil Vicente made it back-to-back wins in their battle against relegation with a 1-0 triumph over Pacos de Ferreira.
Simeon Nwankwo scored the decisive goal against Maritimo last time out and the Nigerian forward came up with the goods again, settling the contest midway though the second half.
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