Guinea-Bissau missed a late penalty as they were held by Sudan in their Group D opener in AFCON 2021.
Midfielder Pele saw his 82nd-minute spot-kick kept out by Sudan goalkeeper Ali Abdalla, with Toni Silva striking the bar on the rebound.
Abdalla had been adjudged to have fouled Steve Ambri inside the area.
Joseph Mendes also twice went close for Guinea-Bissau, heading against the post in the first half and seeing an effort cleared off the line late on.
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Earlier in Group D Kelechi Iheanacho was on target as Nigeria comfortably beat seven-time champions Egypt.
The result means Guinea-Bissau have failed to score in each of their past five Nations Cup matches and now face an uphill battle to reach the knockout stage for the first time.
Sudan, who were appearing in the tournament for the first time in 10 years, seemed content with a point at full-time with interim coach Burhan Tia managing the 1970 champions for the first time in a competitive match.
The East Africans sacked former boss Hubert Velud last month after a disastrous showing in the Arab Cup where they conceded 10 goals and failed to score across their three games.
BBC