Nielsen scored a total 16 goals in 20 games for the Denmark national team,[3] and won silver medals at the 1908 and 1912 Summer Olympics.

Born in Copenhagen, Sophus Nielsen started his senior career with local team Boldklubben Frem.

Sophus was the footballing idol of many Copenhagen youth players, including later Danish international team captain Pauli Jørgensen.

[5] Having served his apprenticeship as a blacksmith with Burmeister & Wain, Sophus Nielsen and his unemployed carpenter brother Carl, decided to travel Europe as journeymen.

Here they met the chairman of the local football club Holstein Kiel, whom Sophus knew from an earlier trip with Frem.

Nielsen's record was matched in the 1912 Olympics, as Germany's Gottfried Fuchs scored ten in a 16–0 win against Russia.

Nielsen would have deployed the wingers in a more defensive role, while having two centre-forwards (anticipating the later 4–2–4 formation), but this was blocked by the rest of the Denmark national team committee.