As they have done for much of this season, City put on a majestic display to give themselves a surely unassailable advantage in a draw against what had been a dynamic and reinvigorated Portuguese champion.
Bernardo Silva was brilliant, silencing the boos that greeted every touch from him and City’s three other former Benfica players with his side’s second and fourth goals, the first a glorious half-volley from a corner.
In-form Riyad Mahrez was on the scoresheet again with a close-range finish awarded via VAR after a long delay to assess whether Kevin de Bruyne had moved offside in the build-up as originally planned .
Phil Foden also added to his growing collection of cool and calm finishes in a relentless first half that shattered Sporting.
There was no respite after the break, with Silva seeing off a header with a hat-trick ruled out for offside before allowing Raheem Sterling to curl in a neat fifth.
The result equals the biggest margin of victory in an away game in the Champions League knockout stage and gives City their biggest European away win, tied with the 5-0 victory at Steaua Bucharest in the play-off round of this competition in 2016-17.
Sporting will travel to Manchester for the formality of the second leg on Wednesday, March 16.