A late equaliser in the 88th minute by Prayag United's Ranti Martins and some crucial misses in front of the rival goal, including one which hit the bar in the last attack of the play, denied ONGC full points in their first home match on October 26.
Nine days later, an injury and a red card to Brown stay a thorn in ONGC's flesh.
"An injury to our defender Bijoy Gurung enabled Prayag to crawl back into the match," said ONGC Coach Subrata Bhattacharya.
"His substitution proved to be the turning point. I had no option as he was injured," he added.
Gurung hasn't yet recovered from his hamstring injury and will have to sit out against Air India.
"We have an adequate replacement. It's the I-League and you need to build your team keeping such mishaps in mind."
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Apart from Gurung, ONGC's goalscorer against Prayag Brown will be missed.
"It was Brown's first match and he had announced his arrival with a superb let-footer freekick which beat Subrata Pal hands down. We will miss him for sure. But such is life," Bhattacharya said.
"Air India are a tough opponent. We watched them in the Federation Cup and there's tremendous cohesion in the midfield. Mohun Bagan were lucky to garner full points against them in their last match," he added. More