I'd use two screens (static or AJAX) or one screen with steps where the second step is disabled (or even better, hidden) until first step is successfully completed.
Basically, instead of having your user wonder what to do or creating distress or friction for the user, you can simply guide the user through steps for succesful achievement of the task. Thus, you give the user one and only one option. If succesful, then the user goes to the next step where he/she will have one and only one option. And so on.
While your scenario is very simple (2 tasks), the friction grows exponentially if you offer different steps on the same level, so I think that whenever you need to use some kind of "user guidance", it's better to use linear processes