It took City just three minutes to double the lead after the re-start.
Such is unbeaten City's dominance at the moment that Guardiola felt the need to make a point of being critical about elements of his team's performance that he thinks ought to be improved.
United only had one shot on target in the game and that was when Martial scored.
With City 3-1 up in the final minutes, Sterling had the ball deep in the United half on the left wing but, rather than take the ball to the corner flag or keep possession, the England forward produced some fancy-footwork stepovers.
Raheem Sterling's cross from the right looked over-hit, but Bernardo managed to hook the ball into the centre of the box where David Silva collected and then fired past De Gea to send the Etihad wild.
The remainder of the half was largely dominated by City, but with no major chances created as the Reds sat back and invited pressure.
The leveller brought relief for the Gunners but for long periods of time, this was a less than convincing performance by the north London club.More news: IS claims responsibility for Australia attack - 11/9/2018 6:02:19 AM
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Jose Mourinho's side barely threatened until substitute Romelu Lukaku came on to win a penalty that Anthony Martial converted just before the hour mark.
Discussing the woeful pass completion stat, Jenas said: "There's no intensity or intent or plan to go and get the ball back actively".
Marouane Fellaini was drafted in to take his place and Mourinho believes the result might have been different had the Belgian been available from the bench with the score at 2-1 before Ilkay Gundogan wrapped up the points with City's late third goal.
It was no more than City deserved. We were stable, we scored one goal, the first 15 minutes was good and after that we didn't press so well. "The last 30 minutes we played really well".
Pep Guardiola's side have now won 11 and drawn one of their last 12 games with the only blip in that run coming in a 0-0 draw away to Liverpool - one of only two fixtures they lost in the Premier League last season.
"I don't like to lose and speak about this player that was not (here), I don't like that very much but he is important for us in many aspects", Mourinho said of Pogba.
Jose Mourinho is never going to be a coach who throws caution to the wind, but his starting lineup for this game gave City the encouragement to push United back from the outset.
The last worldwide break of the year means no game now for fortnight with the champions resuming a week on Saturday away to West Ham United.