Purpose: To identify facilitating and redundant components of core competence development during the growth phases in entrepreneur-driven SMEs. • Methodology: Conducts a longitudinal empirical study based on large number of interviews. • Findings: Describes how individual competences critical for a start-up firm (entrepreneurial, market and network) eventually are transformed into organisational routines and institutionalised. Highlights distinction between competence and organisational structure. The latter could emerge incrementally in a firm, yet also be a tool to manage organisational change. • Research limitations/implications: Brings in-depth knowledge by qualitative analysis. Future studies should test our findings in large-scale study with quantitative analysis. • Practical implications: A start-up built on technology competence needs to combine with market competences, preferably in parallel, or in sequence, for ideal core competence development. To expand further, the entrepreneur ultimately must step down. Important to balance the firm's ambidexterity by adding exploitation to the initial exploration. To boost expansion further, explicate visions and policies must be added, which will guide and release employees' innovative drive. • Social implications: Suggests how entrepreneurial spirits could be transformed to facilitate growth beyond small firm size. • Originality/value: Informs scholars and managers of core competence facilitators during SMEs growth phases.