William set Leonardo Jardim's side on their way after 16 minutes and Montero grabbed his first six minutes after the break.
The away side then had Filipe Anunciacao sent off 19 minutes from time for a foul that resulted in a Sporting penalty and the league's leading marksman Montero duly converted it.
Sporting's win in the evening kick-off knocked Benfica off top spot after they had briefly been there following Lima's late brace gave them a 3-1 win at 10-man Rio Ave.
Rodrigo put Jorge Jesus's side ahead after 38 minutes but they were pegged back through Ukra after 57 minutes.
The Brazilian Lima wrapped up the scoring 12 minutes from time and Benfica's fourth consecutive win in all competitions lifts them above Porto, who lost 1-0 at Academica on Saturday.
Elsewhere, Gil Vicente failed to break down Belenenses, who played for 65 minutes with 10 men following Fredy's straight red card. The result leaves Gil Vicente in fourth, while Belenenses are two points off the bottom two and have not won for three games.
He grabbed his fourth of the season eight minutes before half-time, but Vitoria Setubal would not be denied and defender Javier Cohene rescued a point eight minutes from time, extending his side's unbeaten league run to four.
Paco de Ferreira's heavy defeat lifted Arouca up one place on goal difference, despite their 2-1 defeat at home to Maritimo in a game that saw both sides finish with 10 men.
Arouca rallied and equalised through substitute Serginho, who scored within a minute of coming on. But Arouca's joy was short-lived as Miguel Oliveira saw red for a second booking.
Their misery was compounded by Heldon's second with 10 minutes remaining and although Maritimo's Sami was sent off late on, they held on for a third successive win in all competitions.
