Kassaly twice denied Congo striker Dieumerci Mbokani to make up for an error strewn performance in his country's 1-0 defeat by Mali in their opening Group C match on Sunday.
He dropped a cross that allowed Mali a late winner but on Thursday at Port Elizabeth's Nelson Mandela Bay Stadium did not put a foot wrong as Niger broke new ground.
Although the arid west African country, relative rookies at the finals, secured their first point in the finals after losing all three games in 2012 and their opening match here, the result still leaves them bottom of the standings.
A draw was more damaging to Congo's hopes of progressing, representing a missed chance and means they must now beat Mali in their last group game in Durban on Monday.
Mbokani was twice in the clear in the first half.
His first effort on 13 minutes was blocked by Kassaly after the Belgian-based striker had chested perfectly a cross from Patou Kabungu and swiveled it goalwards.
Kassaly made an even better save after Mbokani had played a clever one-two with Tresor Mputu in the 42nd minute, bravely blocking a powerful shot from close range.
Niger had a chance of their own but it came at the start of the game when Modibo Sidibe rode through a tackle and found himself clear on goal with just Robert Kidiaba to beat but although he hit it wide of the goalkeeper, found the foot of the goalpost.
"It's a missed opportunity. It was possible for us to move forward. We have to concede that after we missed the two chances we did not play well," said Congo coach Claude Le Roy.
Ghana, who beat Mali 1-0 in the earlier game, top the group after two matches with four points, followed by Mali (3), DR Congo (2) and Niger (1).
