FRANCEVILLE, Gabon -Ghana and Mali square off in Group D on Saturday as the African Cup of Nations starts to take shape, even if it's not the shape many expected.

With the surprise success of co-host Equatorial Guinea - the lowest ranked team at the event - and the first-round failure of Senegal, both Ghana and Mali have sights set on passing safely through to the quarterfinals after opening with nervous victories.

But a win for one at Stade de Franceville - in perhaps the tournament's biggest matchup so far - will leave the other with a high-pressure final group game to advance.

In Group D's other fixture, outsiders Botswana and Guinea meet as both search for the win that will close the gap on the frontrunners and maybe set up a jittery finish to the first round for one of the favorites. Ghana's players described the meeting with fellow West African nation Mali as "massive'' and "crucial'' and a "do or die affair'' as neither wants to follow the failure of Senegal, which has already been eliminated after failing to deal with the unexpected threat of Zambia and Equatorial Guinea.

"Before the Botswana game we knew it was going to be tough going in Group D and coming with the tag of favorites the other teams would be keen to catch us cold and knock us out,'' Ghana assistant coach Kwesi Appiah said. "The boys know what is at stake.''

With title rival Ivory Coast already through to the last eight, Ghana's nerves have not been helped by fitness doubts over striker Asamoah Gyan, who limped out of training on Thursday with the right ankle injury he sustained in the 1-0 victory over Botswana.

The forward was withdrawn from training as a precautionary measure, the team said on its official website, and was being "observed'' ahead of Saturday's match. For Mali, which also edged its opener 1-0 over Guinea, 32-year-old Barcelona midfielder Keita has become key in what may be his last chance at international glory. Keita's emotional response to the win over Guinea, when he left the field in tears of joy, underlined what the tournament meant to him.

While a Mali victory wouldn't be the biggest upset of the tournament so far considering Equatorial Guinea's jaw-dropping start, it would be a surprise. "It's a game that we are going to call a do or die affair,'' Ghana defender John Pantsil said. "That's the game that would qualify us to the quarterfinal.'' Fighting to keep alive their chances of a quarterfinal place, Botswana and Guinea play in Saturday's first game at Stade de Franceville with the Botswanans, at the African Cup for the first time, the undoubted outsiders. "Guinea hammered us home and away the last time we played them in qualifiers a few years back so we have to be smart about the game,'' Botswana captain Dipsy Selolwane told The Associated Press. "They (Guinea) are very strong, very powerful, we actually felt they were a little bit stronger than Ghana in their opening match.''

Selolwane is in line for a recall at the heart of midfield for Botswana after being suspended for the opening game. He should boost the team's preferred tactics of defending in numbers and breaking away with quick counterattacks. Guinea has to convert its chances after missing a string of opportunities against Mali if it's to avoid becoming the latest team to join the African Cup's spate of upsets.