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Only Nigeria have impressed of the three title contenders that took to the field on the third day of the Africa Cup of Nations.
The Super Eagles beat Egypt 1-0 while defending champions Algeria were held to unexpected goalless draw against an unheralded Sierra Leone side.
All three of the African giants have won the competition in the past 12 years.
In Tuesday's evening kick-off, Sudan and Guinea-Bissau battled out a goalless in Group D.
A well-taken first-half goal by Leicester City's Kelechi Iheanacho was enough to secure Nigeria victory in Garoua with Mo Salah largely isolated in the Egyptian attack.
Liverpool striker Salah had one chance after 70 minutes but was off balance and his weak shot was saved by Nigeria goalkeeper Maduka Okoye.
Iheanacho crashed a half-volley from the edge of the box into the top corner after 30 minutes to settle the contest, but Nigeria should have scored more.
Winners of the Arab Cup in December, and now unbeaten in 35 matches, Algeria had been expected to sweep away the Leone Stars who last appeared in the competition in 1996.
Despite featuring attackers such as Premier League players Riyad Mahrez and Said Benrahma in Douala, Algeria were unable to beat the outstanding Mohamed Kamara.
Sierra Leone had chances of their own in the first period through Alhaji Kamara but the second half was all Algeria.
One-time England international Steven Caulker -- who was making his debut for the nation of his paternal grandfather -- made a superb block from Sofiane Bendebka as Sierra Leone held on.
While three teams will qualify for the knockout stage from four of the six AFCON groups, the result is a concern for Algeria as they are in a strong Group E that also features Ivory Coast and Equatorial Guinea, who play on Wednesday.
Guinea-Bissau missed the chance to open the tournament with a win after a late penalty from Monaco midfielder Pele was saved and then Piqueti crashed the rebound against the crossbar.
Sudan had made a drastic overhaul of their squad just weeks before the tournament after they lost all three group games at last month's Arab Cup.
They fired French coach Hubert Velud and dropped many of their regulars for the tournament.
Guinea Bissau next take on Egypt while Sudan meet Nigeria in a Group D double header in Garoua on Saturday.