South Africa also had a goal disallowed and struck the crossbar as they just about deserved the victory, but lively Angola had their chances too will be disappointed not to have got something from the game.
South Africa took the lead on 21 minutes when Oswin Appollis showed neat footwork in the box to work a shooting chance and put the ball in the bottom corner of the net, but Angola equalised before the break as Show got a touch to Fredy’s free-kick to make it 1-1.
But the winning moment came on 79 minutes when Burnley’s Foster was teed-up 25 years from goal and curled his shot into the top corner to give the bronze medallists from two years ago a positive start to their campaign.
After Teboho Mokoena fired wide from 35-yards, Foster's header was saved by ex-Cape Town City goalkeeper Hugo Marques.
Angola captain Fredy forced a fine save from South Africa goalkeeper Ronwen Williams with a volley, the latter beating the ball away to safety in a crowded penalty area.
South Africa took the lead after a period of possession that led to Khuliso Mudau’s cross, which was touched by both Sipho Mbule and Foster, before Appollis beat two defenders and side-footed into the bottom corner of the net.
Williams was called into action again when he saved a point-blank header from Gelson Dala via Fredy’s corner.
Angola equalised on 35 minutes when Fredy’s low free-kick was touched into the bottom corner by Show, his second goal in his 50th cap for his country.
South Africa replaced Mohau Nkota with Tshepang Moremi at halftime to try and get more attacking threat on the wing, as he moved to the left and Appollis to the right.
And the change almost paid immediate dividends as Moremi had the ball in the back of the net, but Foster was offside in the build-up and the Video Assistant Referee ruled it out.
South Africa’s Mbekezeli Mbokazi crashed the ball against the crossbar with a rasping shot from 35-yards, before Foster snatched the three points with his clinical finish.
Flashscore Man of the Match: Lyle Foster (South Africa)