Singh moved to the top of the scorers charts in the tournament by netting his fifth goal in a rampant display that underlines his status as one of the country’s bright new stars.
South Africa will now play the Zambians in the final at the Moruleng Stadium on Friday with a 17h30 kick-off (15h30 GMT). Angola will contest the bronze medal with DR Congo at 11h00 (09h00 GMT)
The match was stopped for around 40 minutes by a floodlight failure at the stadium which delayed the start of the season half.
By then South Africa were already winning 2-0 as Singh reacted quickest after Angola goalkeeper Joao Eduardo had fumbled the ball into his path. Menzi Ndwandwe headed a second a minute before half-time.
The home side continued to mount wave after wave of attacks on the Angolan goal and were rewarded when Singh turned his marker and fired home after 57 minutes.
The overseas export and Ndwandwe both added another goal each before the end of the game to take South Africa to within one win of retaining the COSAFA Under-20 Championships title they won in Lesotho three years ago.
[Ed's note: Official scorers of the tournament initially issued the incorrect goalscorer information, which has now been corrected.]