Hamilton, Swan and Klein save the Brainiac/Clayface team up for the last couple of pages of the story in World’s Finest 144 (Sept. 64).
Jimmy Olsen and Robin are far more important to the tale than the villains are. Jimmy winds up doused with microscopic kryptonite by Brainiac, and so he and Robin switch partners. Batman is so happy to be working with Jimmy that he even reveals his secret identity to him!
As the story goes on, Superman finds Robin a less desirable partner than expected as they take on Brainiac, and Jimmy similarly causes problems for Batman as they deal with Clayface.
Matt Hagen only meets Brainiac as the story approaches its climax, in which the two young heroes prove themselves and lead the capture of the villains.
While Brainiac continues to appear frequently, Clayface is reduced to very small roles for the next decade, showing up next as part of a large group of villain working under the Queen Bee in an issue of Action Comics in the mid-70s.