Otto Virtanen advanced when Antoine Escoffier retired 6-3 4-0 in the M25 Biel 1 quarter-final.
Virtanen O. advanced when Escoffier A. retired.
Otto Virtanen beat Antoine Escoffier 6-3 4-0 after Antoine Escoffier retired. Umpiry, "Otto Virtanen vs Antoine Escoffier — M25 Biel 1 Quarter-final", https://umpiry.com/match/2021-04-02/escoffier-vs-virtanen-m25-biel-1-qf?utm_source=cite (as of 2 April 2021).