After Shillong striker Penn Orji was fouled about 30 yards away from the rival goal line, his teammate Boithang Haokip made no mistake in converting the free-kick.
The hosts created chances earlier also but strikers Haokip, Orji and Cornell Glen could not capitalise on them as both sides struggled in the cold weather condition prevailing at the JN Stadium here.
Raids by Mumbai FC players also did not bear fruit and the first half completed with 0-0 score.
After conceding the goal, the visitors got two chances in quick succession but could not score.
