sorry mate, been working on this one and no luck.
I tried sorting Discogs tunes into category:House, year:1988/1987 etc etc to narrow down the search but to no avail.
Even though the event was in 1988 I'm thinking that perhaps this could be an older tune from 1987 or even 1986.
It has that classic piano House sound so possibly made by one of the House legends.
That piano riff is just too good to not be given any recognition on a classic House compilation or documentary somewhere.
I've also wondered if it might be an early Italo House tune.
Have you tried asking Marshall Jefferson if it's his? Even if it isn't he might just happen to know what it is. It's worth a shot.
Or do you know or can you find out who the DJ was that spun this tune at the Mutoid event?