Pep Guardiola wasn't the one in charge of the match, it was his assistant coach "Juan Manuel'' who was in charge of the match(supervised, featured, and made the substitution in the match). This is his first time being in charge of a Manchester City match wouldn't blame him that much since Pep Guardiola went for a back surgery at Barcelona. Although the back surgery has been done successfully.
I was surprised to see Manchester City dominate the match, but they couldn't score comfortably, they found it very difficult to break Sheffield United's defence, but Manchester City was lucky because they managed to score with a goal difference. If Pep Guardiola was present in the match, I am sure he would change the tactic, but the assistant coach didn't really do anything, he made just one substitution in the match. It won't really be easy for Manchester City until their main coach, Pep Guardiola, comes back.
Manchester City's next match against Fulham won't really be an easy one for Manchester City. The assistant coach is not really active, he didn't correct the players in today's match, he made just one substitution, and he didn't do it at the appropriate time. Pep Guardiola's and De Bruyne's absences are really going to affect Manchester City's performance.