Allegro moderato, A-flat major, 3/4 time.

It is in sonata form. The first theme, presented in unison arpeggios, opens in A-flat major. The subsequent soft transition section (from m. 11) leads to a half cadence on the double dominant (the dominant of the dominant), whereupon the second theme is gently presented from m. 19, still softly, in the dominant key (E-flat major). When the second theme is repeated, it becomes more dynamic as the accompanying figuration's note values shorten at mf.

What is noteworthy in the development section is that various motivic manipulations are carried out using material from the transition section, rather than from the two themes of the exposition. In the recapitulation, the opening theme returns in the tonic key, unlike the preceding three piano sonatas where it returned in the subdominant. By recapitulating the transition section in D-flat major after a modulation at m. 71, the second theme is introduced in the tonic key.

Compared to his previous piano sonatas, this movement is smaller in scale, and the frequent modulations in the exposition are restrained. This compositional approach, employing only the bare minimum of motivic material and modulations, is as if Schubert were attempting to compose in a textbook-like form that would later be formalized.