MONROVIA -- Ghana caused an upset by beating Liberia 2-1 away in a World Cup qualifier on Sunday, handing Nigeria top spot in African group B with a 4-0 win in Sudan.

Liberia, overnight leaders in the group, had started full of confidence, dominating for most of the first half before a capacity crowd of 36,000 -- but missing a hatful of scoring chances.

Charles Amoah put Ghana ahead in the 33rd minute, scoring from an Emmanuel Duah pass.

Kelvin Sebwe equalised for Liberia just before halftime after a move set up by former World Footballer of the Year George Weah, also the side's technical director.

But Liberia lost their way after the break and Ghana took control after Isaac Boakye scored on the hour in a goalmouth scramble, slotting past Anthony Tokba. The keeper was standing in for Lours Crayton, who was injured in a car crash last week.

Nigeria crushes Sudan 4-0 to move into first place

In Sudan, Nigeria secured victory with two goals from Yakubu Aiyegbeni and one apiece from Austin "Jay Jay" Okocha and Victor Agali.

The win put Nigeria on 13 points from seven games, one ahead of Liberia with one match each to play -- Liberia away to neighbouring Sierra Leone and Nigeria at home to Ghana.

Third-placed Sudan, on nine points from six games, also have a mathematical chance of qualifying, while Ghana are a point further back.