[T]he neoclassical streak of Prokofiev’s music is expressed in mock Baroque or Classical textures, such as an allusion to Alberti bass in the finale of Sonata No. 5.
Boris Berman, Prokofiev’s piano sonatas : a guide for the listener and the performer (2008), "Prokofiev the pianist"
The Fifth Sonata, written in Paris, differs significantly from both the early sonatas and the later ones. Its musical language shows Prokofiev in his more experimental phase, as do his many other works of this period.
Boris Berman, Prokofiev’s piano sonatas : a guide for the listener and the performer (2008), "Sonata No. 5 in C Major, op. 38 (First Version), op. 135 (Second Version)"
The Fifth Sonata, the Quintet and the Second Symphony, continuing from the Sarcasms through the Scythian Suite and Seven, They Are Seven, were the most chromatic of all my compositions. This was the effect of the Parisian atmosphere where complex patterns and dissonances were the accepted thing, and which fostered my predilection for complex thinking.
Sergei Prokofiev, In: S. I. Shlifshtein, ed., S. Prokofiev: Autobiography, Articles, Reminiscences, trans. Rose Prokofieva
In 1944 to [Prokofiev’s] great joy the pianist Maria Grinberg gave a performance in the Small Hall of the Moscow Conservatoire of his long-neglected Fifth Sonata for piano. After the recital he asked Myaskovsky, who sat next to him, whether there were many ‘false notes’ in the sonata. Myaskovsky replied that ‘all traces of the scarlet fever had disappeared.’ Nevertheless in 1952 before the publication of a new edition of the sonata Sergei Sergeyevich decided to revise it and wrote a new version. He often told me how pleased he was that he had rewritten that sonata.
Mira Mendelson-Prokofieva, In: S. I. Shlifshtein, ed., S. Prokofiev: Autobiography, Articles, Reminiscences, trans. Rose Prokofieva