Congo won their first game at an Africa Cup of Nations finals since 1974, beating Gabon to move top of Group A.
The Gabonese enjoyed the better of the first half but fell behind after 48 minutes when Prince Oniangue stabbed the Red Devils in front from a corner.
Charlton Athletic’s Frederic Bulot, who had a fine early volley saved, wasted Gabon’s best chance, missing an open goal midway through the second half.
A draw against Burkina Faso on Sunday would take Congo to the quarter-finals.
Whoever wins between Gabon and Equatorial Guinea in Bata on Sunday will also qualify for the last eight.
Gabon dominated the early exchanges, playing with confidence after their 2-0 win over Burkina Faso on Saturday.
Just four minutes in, Bulot tested Congo goalkeeper Christoffer Mafoumbi with a blistering volley from the edge of the box, after Malick Evouna teed him up at the end of a fine move.
Fifteen minutes later, Evouna was played in by the influential Levy Madinda and was unlucky to see his effort hit Maffoumbi before ricocheting off Congo defender Dimitri Bissiki and rolling inches wide.
All eyes may have been on Gabon’s Borussia Dortmund star Pierre-Emerick Aubameyang but as he struggled from a wide position, Madinda grabbed the limelight and the bustling midfielder almost gave the Panthers the lead.
Neatly flicking the ball over the head of one defender inside the box, he dragged wide just ahead of the break.
Congo were barely in the game but the half-time team talk delivered by veteran Frenchman Claude LeRoy, coaching at his eighth Nations Cup, galvanised a side contesting its first Nations Cup finals since 2000.
And when Gabon failed to clear a routine corner after the teams’ return, Congo captain Oniangue lifted the ball into an unguarded corner of the net.
Then midfielder Oniangue thumped an 18-yard volley straight at a relieved Gabon goalkeeper Didier Ovono.
After Gabon’s Madinda failed with two chances in a minute, Bulot was left with a moment that may come back to haunt him – firing wide from inside the box with the goal at his mercy.
No coach has overseen more Nations Cup matches than LeRoy, who led Cameroon to the title in 1988, and he added to that record after Madinda squandered yet another Gabon chance late on.
Congo coach Claude LeRoy:
“Our game plan worked well and we were lucky that Gabon did not convert their chances.”
“Hats off to this Congo team for their morale and mental qualities. I’ve practically never had a team that works so well tactically, even if we are lacking in certain areas.
Gabon coach Jorge Costa:
“We had chances in the first half but didn’t have the luck today that we had against Burkina Faso.”