Spiridon Niculescu was born on 8 April 1943 in Vidra, Romania, starting to play junior level football in 1961 at Dinamo București.[1][3] One year later he went to play for Divizia B club, Dinamo Pitești, a team which he helped promote to the first league after one season.[1][3] He made his Divizia A debut on 25 August 1963 in a 2–1 home victory in front of Știința Cluj.[1] At the end of his third season, the team reached the 1965 Cupa României final where coach Virgil Mărdărescu used him as a starter and he conceded a goal from Remus Câmpeanu in the 11th minute, being replaced in the 17th minute with Constantin Matache in the eventual 2–1 loss in front of Știința Cluj.[1][4] In 1966, Niculescu was given in exchange to Dinamo București for fellow goalkeeper Narcis Coman where he played in another Cupa României final in 1968, coach Bazil Marian using him all the minutes in the 3–1 win over Rapid București.[1][3][5][6][7] Afterwards Niculescu returned to Pitești, the team being now named Argeș and started playing in European competitions during the 1968–69 Inter-Cities Fairs Cup, appearing in both legs of the 5–3 loss on aggregate from the second round in front of Göztepe.[1][8] In the 1971–72 season he won the league title with Argeș, but he played just one game as coaches Titus Ozon and Florin Halagian preferred Vasile Stan as first-choice goalkeeper.[1][3][9] In 1973 he went for half of season at Rapid București, playing only two league games.[1] He then returned to Argeș where he made one appearance in a 1–1 with Fenerbahçe from the first round of the 1973–74 UEFA Cup edition but they did not qualify further as the first leg was lost with 5–1.[1][10][11] On 29 September 1975, Niculescu made his last Divizia a appearance in a 2–0 away loss in front of Politehnica Iași, having a total of 145 games in the competition with 216 goals conceded.[1] He completely ended his career in 1976 after he spent one season and a half in Divizia B at FC Brăila.[1][3]