Gary Neville has urged supporters of both Manchester clubs to not "get carried away" by both sides' early-season form.
Jose Mourinho's side have scored four goals in three of those games, while Pep Guardiola's City scored 15 goals without reply in three outings last week - including a win at Feyenoord in the Champions League - but ex-United defender Neville thinks that it is still "too early" in the campaign to jump to any title conclusions.
"I did say at the start of the season that the title would end up in Manchester and the evidence so far supports that, but it's far too early for either club to get carried away," he wrote in his column for Sky Sports News. "You would have said, from the fixtures, United should have been at the top at this stage, but I think the table will start to even out once we see them against tougher sides.
"There are still big questions about both United and City. Can United break down sides? Can Manchester City handle it against more physical sides?
"If you look at United, you saw them make mistakes at Stoke and there were chances for Everton, but ultimately the weaknesses they have shown at the back are covered by a goalkeeper in David de Gea who is absolutely world-class. To me they are looking a lot better than before in terms of breaking sides down and killing off games.
"I think City were always going to be more impressive in their attacking style. The Arsenal of yesteryear were similar to this Manchester City side in terms of playing really exciting football, but the challenge is doing that in tougher games. I think what we want to see is them tested in big games and that was developing against Liverpool before the Sadio Mane red card, so, for now, they've only demonstrated they can dominate the lower teams."
United are enjoying their best start to a Premier League season since 2011-12, when they won the first five of their games under Sir Alex Ferguson.