This match wasn't where they fecked it. It was the bottling they did in the previous 3. City at the Etihad is always a nightmare fixture but it wouldn't be near as much of an issue if they hadn't dropped points in the previous 3 with 2 of those matches coming against relegation level teams.
But this was indeed a proverbial "six pointer".
If my math is right, had Arsenal defeated City in either the of its two matches against City Arsenal would now be on 78 and City on 70. Even with two games in hand and let's assume they take 6 points from those two games, Arsenal would still be points clear.
True, every match counts the same three points as every other, but losing to City last night was the knockout blow. Even a draw would have been a fantastic result for Arsenal. Again, let's see if my math actually works but if it ended a draw Arsenal would now be on 76 and City on 71. City would still have control over their destiny but they would have win every one of their remaining matches through the end to lift glorious trophy. As it stands now, City have plenty of room for slip ups even if Arsenal take 15 points from their remaining five matches, which now looks very much in serious doubt given the psychological beating they now have to endure knowing they've bottled it after being destroyed by City.