It is only the second time Celtic have failed to win at home this season.
Phunya Sele Sele looked set to win a fifth home game from six attempts after Prince Hlela had handed them the lead in the 71st minute, but Zeka Karkee scored in the 84th minute for Vasco to see the game end 1-1.
Vasco came into the game full of confidence (having won their three previous league matches) and they started the better of the two teams.
Celtic were first to threaten, with Hlompho Kekana firing a thunderous low drive just wide of the target after being teed-up from a free-kick in the 14th minute.
The visitors’ passing and off-the-ball running was impressive, but they did not create many scoring chances in the first-half, mainly because lone striker Excellent Walaza looked isolated.
Walaza had a great opportunity in the 21st minute but he scuffed his shot and Patrick Tignyemb was able to make a good save low to his right.
The best chance of the first half went the way of Celtic’s Nathan Paulse, who had a clear sight of goal on 27 minutes, but he placed his shot too close to Omony.
Celtic got into their stride in the final few minutes of the half. Dennis Kalala, Danny Venter and Thokozani Mshengu all had scoring chances, but the score remained 0-0.
In the second half, Omony got in the way of Prince Hlela’s dangerous cross into the box after a barnstorming run down the left flank.
Soon after, Hlela netted his fourth League goal, handing Celtic a 71st minute lead. The young defender scored with a deflected header at the near post after Vasco had left him unmarked from a corner-kick.
Vasco fought back valiantly and brought themselves level in the 84th minute.
A hopeful ball into the box was headed back across the penalty area by Mokete Tsotetsi and midfielder Zeka Karkee arrived late in the box to power a header past Tignyemb, onto the inside of the post and over the goal line.
With just two minutes to play there was a mad scramble in the Vasco penalty area, but Moses Spandeel was denied by a superb reaction save from Omony.