Adrien Silva got the hosts off to a marvellous start, turning inside the area and coolly slotting past Mika in the Boavista goal with just 15 seconds on the clock, the division's fastest goal of the of the season.
The away side hit back just six minutes later, though, as Ze Manuel burst in front of his marker and headed beyond Rui Patricio.
A straight red card for Tobias Figueiredo on the stroke of half-time put Sporting into a tricky situation, as the 21-year-old brought down Leozinho when through on goal.
But, Islam Slimani restored Sporting's lead just after the hour mark, nodding in Andre Carrillo's right-wing cross and Boavista – who had Philipe sent off for two bookings in as many minutes towards the end – never recovered.
Providing Sporting's head-to-head advantage over Braga remains intact after their meeting on May 17, Marco Silva's side only need to collect five more points from their remaining games to secure third place.
At the other end of the table, Penafiel's days as a Primeira Liga club appear numbered, as a 2-0 defeat at home to fellow strugglers Arouca left them seven points adrift of safety, while Gil Vicente – the other team in the bottom two – drew 0-0 with Rio Ave.
Vitoria Setubal did little to allay their fears of relegation, losing 2-1 to visitors Estoril to stay just five points ahead of Gil Vicente, while Pacos Ferreira and Moreirense played out a goalless draw in the day's only other match.
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