Engineers say they have now managed to fully focus the $10bn observatory on a test star. The pin-sharp performance is even better than hoped, they add.
To get to this stage, all of Webb's mirrors had to be aligned to tiny fractions of the width of a human hair.
But the agency cautions that a lot of work still lies ahead before the telescope can be declared operational.
Lee Feinberg, the Nasa engineer who has led the development of Webb's optical elements, described the release of the first properly focused image as phenomenal.
"You not only see the star and the spikes from the diffraction of the star, but you see other stars in the field that are tightly focused, just like we expect, and all sorts of other interesting structure in the background," he told reporters.
"We've actually done very detailed analysis of the images we're getting, and, so far, what we're finding is that the performance is as good if not better than our most optimistic prediction."