Guess what the back-up story in Classic X-Men #17 does? It shows us that.
The way in which Mesmero managed to bring Jean Grey under his thrall was by... walking up to her on the street. That's it. He may as well be bloody Hypnotoad. Then, he decides to see what else he can do other than get her to wait on him hand and foot. Because what Jean Grey totally needs here at this point in her arc is an attempted rape story retconned in. It's made clear on panel the attempt never gets further than the mindcontrol failing. Annoyed at that, he gets Jean to tell him where the X-Men live, and goes to pay them a visit.
There he goes and Hypnotoads them, one by one. Wolverine is the last to hold out, but he falls in the end. And then, Mesmero has effectively won. He's succeeded where many have failed before: he has defeated the X-Men utterly. And he's bored. So, then he gets the idea to set up the circus.