Research linking music analysis and performance has recently focused on the performers’ own analytical insights and their influence on interpretive choices in performance. Here, we examine harpsichordists’ performances and analyses of an unmeasured prelude, the Prélude non mesuré No. 7 by Louis Couperin (1626-1661). The unmeasured prelude, a genre cultivated especially in France between 1650 and 1720, is characterized by a lack of metrical structure and notated durations. Thus, in comparison to musical genres which specify meter and rhythmic durations, it affords the performer a greater degree of expressive freedom, making it ideally suited for investigating the link between temporal patterns and formal structure. Our aim is to more clearly define a link between analysis and performance by investigating how performers convey their sense of phrase structure through their expressive use of tempo variations as well as changes in articulation or velocity. Twelve professional harpsichordists from the Montreal area performed the Prélude non mesuré No. 7 in a recital setting and submitted their own analyses of the piece, indicating its main formal subdivisions. The harpsichord was equipped with a MIDI console, allowing a precise measurement of performance parameters. Although there was some agreement on the main structural boundaries, performers used different strategies to convey their structural interpretation of the piece; in addition to “phrase-final lengthening”, harpsichordists tended to slow down before and accelerate through phrase endings. On a more global level, harpsichordists conveyed a sense of large-scale structure through the amount of tempo variability.