[2] In 1915, Hammarby IF established a football section after a merger with Klara SK, where Wihlborg had started to play as a youngster.

On 15 August the same year, Wihlborg scored in the club's first ever football match, in a 5–0 home win against Västerås SK.

[3][4][5] Wihlborg soon established himself as one of Hammarby's key players, together with goalkeeper Victor Olsson and striker Gustav Björk.

[9] In 1922, Hammarby had an other strong showing where they went to the finals of Svenska Mästerskapet, a cup by then held to decide the Swedish champion, losing 1–3 to GAIS in a game where Wihlborg captained his side.

[11][8] Wihlborg was one of the first players from Hammarby IF to establish himself as a member of the Sweden national team,[12] and debuted in a 3–3 friendly draw away at Finland on 28 September 1919.