As a city fan living in Istanbul, my suggestions to you are,
Kadıköy-Bağdat Street (places close to the Kadıköy area) is the most decent and safe area of Istanbul, where you can have a nice meal and a beer before the match and have a quiet and pleasant time. If you stay at the hotel in an area close to Bağdat Street (esp goztepe-erenköy and suadiye district), you can spend the whole day in wonderful restaurants and bars.
Alternatively, you can have a good time in the squares of Kadıköy and Beşiktaş, but these areas will be very crowded.
If you have questions about the regions, I can help.
I'll be in the stadium, I hope we win.