Algeria and Senegal secured come-from-behind victories on Monday as the Africa Cup of Nations group of death sprang to life with seven goals in a Mongomo double-header.
Title favourites Algeria trailed South Africa and could have been even further behind before an own-goal set up a 3-1 Group C triumph.
Slow-starting Senegal also trailed only to snatch a 2-1 win over Ghana via a Moussa Sow goal three minutes into stoppage time.
The results left Algeria top of the table on goal difference and, if they defeat Ghana on Friday and Senegal conquer South Africa, the battle for last-eight places will be over.
An impressive 2014 World Cup campaign and five consecutive qualifying victories elevated Algeria to the unwanted role of favourites among the media.
But for 65 minutes at a packed 15,000-seat Estadio Mongomo in eastern Equatorial Guinea, a South African side boasting an unbeaten 10-match record under coach Ephraim 'Shakes' Mashaba had the edge.
Captain Dean Furman slammed a first-half shot off the woodwork and after Thuso Phala put Bafana Bafana (The Boys) ahead, Tokelo Rantie watched his spot-kick fly over off the crossbar.
Algeria then piled on the pressure and Thulani Hlatshwayo headed a cross into his own net before Faouzi Ghoulam and Islam Slimani scored for the rampant Desert Foxes.
France-born Algeria coach Christian Gourcuff said: "The penalty miss was a turning point because at two goals behind we would have been in trouble.
"I would have liked more control of the game ... we lacked rhythm at times."
Mashaba, meanwhile, was upbeat despite his first loss in the job: "The best team lost. We created a lot of chances in the first half, but after missing the penalty everything went awry."
- Sluggish -
Earlier, sluggish Senegal fell behind when goalkeeper and captain Bruno Coundoul fouled Christian Atsu and Ghana captain Andre Ayew calmly converted the penalty.
Atsu wasted a great chance to add a second goal before a Kara Mbodj header rebounded off the crossbar to signal a Teranga Lions revival.
Ghana battled to contain the tall Senegalese strike force after half-time and Mame Biram Diouf levelled just before the hour by nodding in at the second attempt after his first header hit the post.
Diouf wasted two good chances to put his side ahead before Sow struck at the death as Senegal claimed a first Cup of Nations victory over Ghana at the fourth attempt.
Coundoul booted a free-kick toward the Ghana goalmouth and when the ball was weakly cleared, a couple of slick passes set up Sow to fire low past Razak Braimah.
Senegal coach and former France star Alain Giresse later warned his players against becoming overconfident as the Lions hunt a first Cup of Nations title.
"It is always better to take three points, but it does not mean that we are guaranteed to qualify, just as the defeat for Ghana does not mean they are eliminated," he said.
"At half-time I told the players that nothing was lost. We went back onto the field with conviction."
Avram Grant, the former Chelsea manager debuting as Ghana coach, said: "It was a difficult match for us.
"We were playing against experienced and very physical players."
Elsewhere, Zambia, who drew 1-1 with the Democratic Republic of Congo Sunday in Group B, have lost Nathan Sinkala for the rest of the tournament.
A knee ligament injury will sideline the Switzerland-based midfielder for at least four weeks and tournament rules do not allow for a replacement.
The Cup of Nations continues Tuesday in Equatoguinean capital Malabo with Group D match-ups between Ivory Coast and Guinea and Cameroon and Mali.