Bata - Congo surged back from 2-0 down and into the semi-finals after beating Republic of Congo 4-2 in an African Cup of Nations thriller on Saturday.
Dieumerci Mbokani scored his second in stoppage time as Congo responded with four goals in the last 25 minutes to deny their neighbours and namesakes.
Both Congos reacted to a lackluster first half with a pulsating second 45 minutes at Bata Stadium in the first knockout game.
Dore Ferebory gave Republic of Congo the lead in the 55th when he drifted in behind the defense at a free kick and flicked home a right-foot volley.
Thievy Bifouma made it 2-0 seven minutes later after some chaotic defending led to him sweeping in a loose ball from close range for his tournament-leading third goal in four games.
Congo, which hit the crossbar twice and had a good penalty appeal turned down, then took over as its opponents suddenly folded.
Yannick Bolasie created the first goal for striker Mbokani three minutes after Republic of Congo's second. He sped down the left, beat his defender to the byline, and pulled back a cross to give the big striker an easy tap in.
Mbokani's forward partner, Loteteka Bokila, equalised with 15 minutes left, powering a shot into the roof of the net after his first effort was blocked.
Substitute Joel Kimuaki headed in a third from a set-piece with nine left in regulation, and Mbokani bore down on goal in the dying seconds to force the ball home and make sure of Congo's place in the last four for the first time in 17 years.
The game had been sedate at best in the first half, with a couple of half-chances for each.
But it exploded into life after the break, with both former champions searching for a long-awaited return to the last four after slipping out of African football's elite over the last few decades.
Republic of Congo appeared destined to make its first semis since 1974, after leading by two with less than 30 minutes to play.
Congo goalkeeper Robert Kidiaba yelled furiously at his defenders for the lapses that led to both of Republic of Congo's goals, but was briefly reduced to tears of joy, and hugging one of those defenders when Kimuaki headed in the third to turn the game.
Sapa-AP