Africa Cup of Nations down to the final four: Who will reach the final?

The Africa Cup of Nations is down to its final four. Nick Ames takes a look at the semifinal matchups, and reveals who of Senegal, Tunisia, Nigeria and Algeria will be moving on to the final.

Algeria vs. Nigeria

Backstory: Until their dramatic shootout win over Ivory Coast, Algeria's run through AFCON had been as sleek as they come. They did not concede a goal until Jonathan Kodjia's equaliser for the Elephants, and looked the tournament's most complete team in all departments. A firing attack and well-balanced midfield saw them win their first four games with little trouble before that nail-biting penalty triumph in the quarterfinals.

For Nigeria the road has been rockier, a group-stage defeat to Madagascar prompting plenty of soul searching around Gernot Rohr's camp. They then came through a hugely entertaining last-16 meeting with Cameroon, turning around a deficit to win 3-2, and overcame a buoyant South Africa 2-1 in a game they should have won more comfortably.

How they match up: Djamel Belmadi's Algeria have been consistently impressive. They have a pest of a striker in Baghdad Bounedjah; creative flair in Riyad Mahrez and Youcef Belaili; a well-balanced midfield axis in Sofiane Feghouli, Ismael Bennacer and Adlene Guedioura; and a defence that gives little away. They will probably miss the dynamic Nice right-back Youcef Atal, though, after he picked up an injury against Ivory Coast, and there is a strong sense their back line could wobble if properly tested, as the Ivorians managed to with their pace.

Nigeria's attacking options are perhaps the best remaining in the tournament. Odion Ighalo, Alex Iwobi, Ahmed Musa and the exciting Villarreal winger Samuel Chukwueze have all made big contributions so far and they are a compelling proposition when attacking at speed. But their defence has consistently made rickets at times when they have appeared to be in control -- and Algeria will certainly have taken note.

Algeria's star to watch: Mahrez has had an up-and-down tournament but has still been influential, scoring twice and offering impassioned words of advice to his teammates before Thursday's shootout. Algeria have already purred as an attacking force but there is a feeling that, if the Manchester City man begins operating at his very best, they might just become impossible to stop.

Nigeria's star to watch: Iwobi remains a curious player whose true level, certainly in the Premier League, looks uncertain. But when Nigeria get him into the right areas he can wreak havoc, just as he did against Cameroon when playing close to the centre-forward Ighalo. He scored the winning goal that day and certainly has another decisive impact in him.

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Algeria's X-factor: Some around the Algeria team believe Belaili is among the most talented players the country has ever produced. Had he not been handed a two-year ban for cocaine use between 2015 and 2017, then perhaps he would be better known beyond Africa; the 27-year-old plies his trade for Esperance in Tunisia these days but he has been on magical form this summer. Goals against Senegal and Guinea were vital; his quick feet and sharp brain have given the Fennec Foxes an extra dimension.

Nigeria's X-factor: The 20-year-old winger Chukwueze broke his international duck with the opener against South Africa and surely there will be more to come. A rapid dribbler full of tricks and purpose, he remains something of a surprise package on this stage and, in an attack full of established stars, may provide the freshness to cause Algeria problems. Pace and purpose certainly troubled them when Wilfried Zaha & Co. found their stride in the quarterfinals.

Algeria need to ...: Keep their heads. They are nearing a first continental title since 1990 and the emotions, when the finally came through against Ivory Coast, poured out long into the night. But they have a habit of getting distracted during games, sometimes getting into needless scraps and niggles, and players like the firebrand Bounedjah tend to operate on the edge. If they master the occasion well, they should have enough to win.

Nigeria need to ...: Tighten up at the back, in order to give themselves any chance. They let both Cameroon and South Africa run them dangerously close after lapses of concentration despite dominating those games, and Algeria -- who are significantly better than both -- will punish them ruthlessly if they fall asleep again on Sunday.

Prediction: Algeria still look the better-balanced team and, while Nigeria's dynamism up front will be troublesome, the north African side should come through with a 2-1 victory.

Senegal vs. Tunisia

Backstory: Senegal have glided to the semifinals, and to within two games of a first Africa Cup of Nations success, with a minimum of fuss. Aside from a group-stage defeat to Algeria -- when they were missing four key players -- they have rarely been troubled, winning their knockout games against Uganda and Benin by deceptively narrow margins of a goal apiece.

It has been 15 years since Tunisia won their only AFCON, and they were not tipped to threaten a repeat this time. That remained the case after Alain Giresse's side ground their way through the group stage with three draws, but a shootout win over Ghana and commanding 3-0 dismissal of surprise package Madagascar suggests they are hitting form at the right time.

How they match up: Nobody enjoys playing Senegal, a physically fearsome side who give little away at the back. Uganda, in particular, found that their own pretty football constantly ran against a brick wall in the forms of Idrissa Gueye, Kalidou Koulibaly & Co. In fact, defensive midfielder Gueye scored a fine winner against Benin in the last eight and, when they do spring forward, an attack including the likes of Sadio Mane and Ismaila Sarr has few peers.

Tunisia have a reputation for an almost Italian brand of defensive football but have expressed themselves more freely in their past two games. Wahbi Khazri, the former Sunderland forward, has been influential while the brilliant Youssef Msakni, who scored against Madagascar, appears back to his best. If Giresse can strike the correct balance in their sternest test yet, they could be more than simply awkward opponents.

Senegal's star to watch: It is Mane, of course, and there is an extent to which this tournament now depends on a few killer flourishes from the Liverpool man in the absence of Mohamed Salah. So far his AFCON has been mixed: Mane has scored three times but missed two penalties, and the room for further slip-ups is getting narrower at this point.

Tunisia's star to watch: Khazri, who plays just off the centre-forward, is the man everything goes through. He takes the set pieces and pulls the strings, playing with a verve and confidence rarely seen during his time in the North East. Can he find spaces between Senegal's lines where other foes have so far failed?

Senegal's X-factor: When Senegal faced Algeria without Gueye, who was briefly sidelined, the difference was glaring. The Everton midfielder gets better and better; his energy levels are phenomenal and his impact on this team, screening the back line and starting attacking moves in transition, is arguably as big as Mane's. If he stays fit and in form, then Senegal have a dynamo who can drive them all the way to the trophy.

Tunisia's X-factor: There is little doubt that Msakni could have played for one of Europe's top sides. It is probably too late now -- he turns 29 in October and played on loan at Belgian club Eupen last season after missing the World Cup with a serious knee injury -- but the Qatar-based schemer remains among Africa's top talents. On a good day he can rip teams to shreds and, if he has one on Sunday, then he can win that battle with Senegal's gnarled enforcers.

Senegal need to ...: Score the second goal. They should have put Uganda firmly to the sword after Mane's early goal, but he missed a spot kick and the outcome remained in doubt until the end. Benin were also well in contention until late on, and if Aliou Cisse's side can show the same level of attacking vigour once they have gone a goal up -- and, of course, if they do -- then they are capable of putting this match well beyond the Tunisians.

Tunisia need to ...: Pick their moments. They have the attacking players to hurt Senegal, but leaving space in behind for Mane & Co. would be a disaster. If they stay compact and fairly deep then the Teranga Lions, who are short of guile in midfield, could become frustrated and resort to hopeful long passes.

Prediction: It will be tight and almost certainly won't be very pretty, and Senegal might just do without that second goal. The smart money is on them edging through with a third straight 1-0 win.