The draw saw Siwelele move up to the 10th spot on the league standing, while Usuthu remained ninth on the table.
Usuthu were the better side in the opening stages of the match and they threatened first through Siyethembe Sithebe.
The dreadlocked attacking midfielder was fantastically denied by Celtic goalkeeper Jackson Mabokgwane 10 minutes into the game.
The visitors continued to launch attacks and Sithebe looked the likeliest player to score for the KwaZulu-Natal giants, but he could not take his chances.
Sithebe had a glorious opportunity to put AmaZulu on the lead in the 26th minute, but was brilliantly denied by Mabokgwane.
Usuthu were left to rue their missed chances as Phunya Sele Sele broke the deadlock four minutes after the half-hour mark.
Mzwanele Mahashe was the man, who scored as he headed home Lantshane Phalane’s free-kick to make it 1-0 to Celtic.
Siwelele then pushed for the second goal of the match and they were awarded a penalty after Ndumiso Mabena was fouled by Tsepo Masilela on the stroke of half-time.
Mabena dusted himself down and he missed the target from the spot-kick and the score was 1-0 to Celtic at the interval.
Usuthu applied some pressure on Phunya Sele Sele after the restart with Augustine Mulenga combining well with Sithebe in the opposition’s half.
AmaZulu deservedly levelled matters four minutes after the hour-mark with Mulenga making it two goals in as many league matches.
Sithebe set-up the Zambia international, who burst into the opposition’s box, before beating Mabokgwane with a decent finish to make it 1-1.
Celtic head coach John Maduka reacted by introducing Tumelo Mangweni as the home side searching for the late winning goal.
Both teams launched attacks in the latter stages of the match with AmaZulu coach Benni McCarthy having introduced striker Somila Ntsundwana.
However, Celtic and AmaZulu were unable to find the back of the net and ultimately, the match ended in a 1-1 draw on the day.
Celtic (1) 1 (Mahashe 34′)
AmaZulu (0) 1 (Mulenga 64′)
Celtic: Mabokgwane, Fikizolo, Chabalala, Mahashe, Lingwati, Pfumbidzai, Phalane (Mangweni 75′), Mashikinya, Letsoalo, Mabena, Njoti (Luthuli 46′).
AmaZulu: Mbatha, Sikhakhane, Masilela (Nyongo 82′), Mzava, Gumede, Ncube, Sithebe, Mlambo (Magubane 64′), Memela (Chawapiwa 46′), Mulenga, Majoro (Ntsundwana 82′). Psl.co.za