The results have pleased manager Guardiola but he is still not satisfied, as shown in the visible signs of frustration he displayed during a scoreless opening 44 minutes of Saturday's 5-0 defeat of Palace.
Meanwhile Mendy's opposing full-back Kyle Walker is relieved he no longer has to deal with the "nightmare" threat of Sergio Aguero in games.
The main focus will be on securing a victory that would move City clear at the top of the group, but the side story involving Aguero could command the headlines.
Walker said: "To play against he is a nightmare". For us, they are absolutely important. "We're professionals and all the players are here to win games and when they win, their lives as professionals are better". You see what he has done in the Premier League.
Manchester City have played 37 games in the UEFA Champions League, none of which have ended goal-less.
After the 6-0 dismantling of Watford, Guardiola spoke of his happiness and how he believes this season's opening good form is more substantial than last season's. He will get a chance to pull level with the club record mark of Eric Brook, which has stood since 1939, at the Etihad Stadium.
'So I think it is going to push all three of us.More news: Does NKorean H-bomb threat push US closer to war?
Napoli reached the last 16 for only the second time last season, but are under serious pressure after their loss to Shakhtar.
Asked whether City's performances would strike fear into their opponents, Guardiola sharply replied: "Chelsea won 4-0 at Stoke City".
All four teams in the group have one point, after Spartak Moscow drew 1-1 at Maribor.
"People say, "Napoli, it's not Milan or Juventus" and, "Shakhtar, it's Ukraine", but this group is tricky".
Captain Vincent Kompany is still not fit to return for the game at the Etihad with a calf strain while Ilkay Gundogan is also out but is back in training after his knee injury scare against West Brom last week.
Paulo Fonseca admits his Shakhtar side face a daunting task.
Fabian Delph, who had an outstanding game at left-back for City, fired an audacious shot just wide before Sterling had a late spot-kick claim turned down, but he got his name on the score-sheet when he side-footed Bernardo Silva's cross high into the net to seal the victory in the 90th minute.
Srna is Croatia's most-capped player with 124 appearances, and made the decision to retire from global football last year after a 14-year stint that included him captaining the side from 2009 to 2016.