It was a Saturday night gig at the University, not fantastically well attended - around 100 people I think.
We (White Unicorn) soundchecked first then sat and listened to Yes run through a couple of songs in the afternoon - one of the songs was 'Looking Around', I think the other was 'I See You'.
I know 'Every Little Thing' was in the set that night - not sure what else apart from the two already mentioned.
I remember how strong the vocals were - a very distinctive sound with Jon's high lead vocal blending with Chris and Pete's harmonies.The band had a much more melodic sound than a lot of what was around at the time (blues based progressive rock and endless improvised instrumental departures!) Yes were very tight and well rehearsed with a strong but light sound - almost jazzy at times with the walking bass lines and Bruford's polished drum style. Apart from the great vocals I think the tightness of the rhythm section was what I remember most and of course Chris Squire's piercing Rickenbacker bass tone - which was so loud it was almost painful!
I don't think they had any lighting and as far as I remember our lighting guy did some for them (White Unicorn used all that projected exploding oil colour stuff but for Yes he just used the basic onstage flashing colours!)
White Unicorn played a lot of other gigs with name bands around this time including John Mayall's Bluesbreakers, Family, Fairport Convention and the Crazy World of Arthur Brown (at Middle Earth in Covent Garden) and of course Pink Floyd.