Colombian striker Fredy Montero grabbed a goal in either half to take his tally to 13 league strikes in 12 games as Leonardo Jardim's side moved above rivals Porto and Benfica on Sunday.
Their challenge was made a little easier midway through the second half when Pecks was shown a straight red card, but Sporting were never troubled as they recorded a fourth consecutive victory to take an outright lead of the Portuguese top flight for the first time since January 2005.
Elsewhere, Rio Ave ended a run of two consecutive defeats as they beat struggling Olhanense 1-0 at the Estadio Jose Arcanjo.
The visitors controlled the game from the outset, but only edged ahead after Anthony Seric was dismissed for Olhanense in the 72nd minute. Ukra was Rio Ave's matchwinner as he netted his second league goal of the season with 11 minutes to play.
Sunday's other Primeira Liga fixture saw Nacional's winless run extended to five games as they were held to a 2-2 draw by Maritimo.
Nacional found themselves behind after only 11 minutes as Heldon netted for the hosts, but Diego Barcellos was able to equalise midway through the first half.
The visitors were reduced to 10-men just after the hour as Fernando Marcal was dismissed for two bookable offences, and they appeared to have thrown away their point when Heldon grabbed a second from the penalty spot with six minutes remaining.
However, Nacional were not finished as Zainadine Junior popped up in the 87th minute to rescue a draw.
