It was not my first derby, but certainly my favourite. It was in 1968 in the latter stages of City's title win. I was working in Sunlight House on Deansgate at the time and a fair group of us went to the match together. We were in the stand next to the Stetford End in the paddock below the seating. The group I went with included some City supporters some for United and some (maybe?) neutrals. Back then with pay-at-the -gate and no segregation, this was possible.
United had an implausible big lead in the table at the turn of the year. Malcolm Allison responded by declaring that 'United were rubbish'. This provoked derision on the press but may have stimulated doubts within United and City closed in.
This Old Trafford derby was arguably the turning point of the season, United went ahead very early on through George Best but City were not phased and pressed on and Colin Bell equalised. City took the lead through George Heslop before Francis Lee settled things at 1-3.
That match flushed out the United supporters I had worked with for some years but had always denied their partisanship. City winning opened up the championship race that season. City took full advantage and (eventually) won the title at Newcastle.