The right-back, aged 17 years and 346 days and making his first senior start, provided the spark for an unusually sluggish City on Wednesday by hitting a superb equaliser at the Etihad Stadium.
Rafa Mir had given the Spanish side a surprise lead but City stepped up after Lewis’ leveller early in the second half and went on to win convincingly with strikes from Julian Alvarez and Riyad Mahrez.
There had been nothing riding on the game with City already confirmed as Group G winners and Sevilla heading to the Europa League from third place.
Consequently the first half was a largely forgettable affair, notable only for Mir’s well-taken header.
City typically dominated possession but, amid torrential downpours and a flat atmosphere, they rarely got out of first gear.
It was not because of a lack of star quality. Erling Haaland again was not risked due to injury and Kevin De Bruyne was among the players benched as Guardiola made seven changes, but the side fielded was still packed with senior internationals.
Only Lewis, fellow youngster Cole Palmer and goalkeeper Stefan Ortega were not first-team regulars.
City were also gifted a handful of opportunities by Sevilla’s unconvincing keeper Yassine Bounou but they could not take advantage with Palmer shooting over and Ilkay Gundogan having an effort blocked.
City were stunned on the half-hour as Mir was left unmarked at the back post to meet Isco’s corner with a firm header which looped past Ortega.
Jack Grealish did force a save from Bounou in response but it was not until the second period they found a spark.
It was Lewis who provided it as he made the latest of a series of runs into Sevilla territory. When the visitors failed to clear, Alvarez played the teenager in on goal and he finished like a veteran with a firm shot past Bounou.
City almost took the lead moments later but this time Bounou clawed out Ruben Dias’ firm header from under the crossbar.
Guardiola decided to increase the tempo further by introducing De Bruyne in the 70th minute and within three minutes the Belgian playmaker had created the goal that put City ahead.
De Bruyne picked out Alvarez with a superb pass behind the defence and the Argentinian coolly swerved round Bounou to tuck home.
Alvarez was not finished there and he set up the third as he robbed a Jose Carmona and teed up Mahrez.
City had late chances to add a fourth but Bounou saved from Dias and Phil Foden.
Additional reporting from PA