The capital club have lost just twice all season - to leaders Benfica and third-placed Porto - and followed up their crucial victory over the reigning champions last week with a comfortable win at the Estadio dos Barreiro.
Adrien Silva got them off to the perfect start with a third-minute penalty after Carlos Mane was tripped by Marcio Rozario, but they were not ahead for long.
Liberia international Theo Weeks levelled the score just three minutes later, rounding off a delightful free-flowing move, but the away side restored their one-goal lead shortly before the break as William Carvalho smashed in from close range.
Jefferson then added a late third, striking from an acute angle after a rampaging run down the left flank, moving his side to within four points of Benfica, who have a game in hand.
The day's earlier kick-off saw Vitoria Guimaraes and Gil Vicente go head-to-head at Estadio Dom Afonso Henriques as the home side eye a late push for the final UEFA Europa League spot.
Guimaraes went into the encounter on the back of a four-match winless run, but they had no problem dominating proceedings as they produced 22 shots compared to Gil Vicente's four.
But they could not find the breakthrough and the match ultimately finished 0-0.
