Ezenkosi claimed the last Ziwa Mo quarter-final spot at the Sinaba Stadium with first-half goals from defender Ousmane Berthe and midfielder Tshediso Tukane.
Carrying a 2-0 lead after the break, the final nail in the coffin was hammered in by midfielder Katlego Loke in the 65th minute, giving the home side an elusive first victory of their 2011/12 campaign.
"God and our ancestors were on our side tonight," proclaimed Sono in the post-match interview. "I was wondering when we were going to win a game... even those (teams) playing on Sundays were winning."
The Benoni-based outfit remain bottom of the Premiership table, but the Black Prince believes Wednesday's success will prove the catalyst for big things to come.
He added: "It is a big boost beating a team like Celtic. (Now) the team will now believes me when I say we're better than half the teams in the league."
Man of the Match Loke reiterated his coach's positive outlook, saying: "The win gives us confidence going forward. It is a turning point for us and we will start using it in the league."
Meanwhile, Celtic coach Clinton Larsen was scathing of his side's performance, but gave credit to Cosmos for their achievement.
"They (Cosmos) played well on the counter and took their free-kick chances when we gave them to them," he said.
"(But) we didn't pitch up on the day and didn't deserve the winning result. We just weren't good enough."