Objectives: The study focused on promoting expressive phonological skills in 1 Greek-speaking child with autism spectrum disorder (ASD) and comorbid speech sound disorder (SSD). Based on the phonological neighborhood density framework, it was hypothesized that the experimental manipulation through clinical implementation of phonologically overlapping stimuli would yield positive expressive phonology gains relevant to ASD. Participant and Methods: A multiple-baseline single-subject design was implemented. Three baseline sessions measured expressive phonology variables. Sixteen biweekly 30-min intervention sessions were carried out for a period of 2 months. Dependent variables included phonetic inventory size, proportion of consonants correct, occurrences of phonological processes, and percentage of whole word matches elicited via specific word probe stimuli. The Intelligibility in Context Scale was completed by the child's teacher prior to the initiation of intervention and at a follow-up session. Experimental stimuli were grouped together in phonologically dense cohorts. Results: Comparison between pre-test and post-test measures revealed expressive phonology gains across all measured variables. Follow-up session results showed generalization of expressive phonology gains on untreated targets. Conclusions: Significant expressive phonology gains were achieved through the implementation of phonologically similar word stimuli within a systematic intervention protocol with the implementation of specific word-level variables. The findings supported this treatment approach for a child with ASD and SSD, while providing evidence for the phonological density advantage from a cross-linguistic perspective.