I was closing in on his Nexus with an army consisting mostly of Artemis and Apollo cruisers.  The units that the AI usually has at home started to come out--then went back--and out and back.  This kept up until they were dead--they never got close enough to fire a shot.

It's possible this was a visibility issue somehow as aircraft were also showing up and getting blown out of the sky, but if so the timing was surprising.  I was within one of his regions but all the buildings there were destroyed and I don't think he could see me from there.  I do not know if he had radar or not as his buildings were dying generally beyond my visibility range.