Thomas Laranjeira's last-gasp penalty handed Brive a potentially crucial 21-18 victory over Connacht in Pool One of the European Challenge Cup on Saturday.
Connacht, top of the pile heading into the penultimate round of games, appeared likely to snatch victory when John Muldoon's second try levelled the score with two minutes remaining.
However, Jack Carty missed the resulting conversion attempt and his side were then penalised, enabling Laranjeira to kick a three-pointer that sent Brive to the summit.
Brive's last pool match will see them travel to Newcastle Falcons, who suffered a damaging 24-7 defeat against Russians Enisei-STM - Connacht's final opponents.
Challenge Cup holders Gloucester will be at home in the quarter-finals of this year's competition after beating La Rochelle 20-10 at Kingsholm.
A fifth win from as many matches for Gloucester was secured by tries from Rob Cook and Billy Twelvetrees.
Elsewhere in Pool Four, Zebre completed a double over Worcester Warriors with a shock 22-15 win at Sixways.
Grenoble leapfrogged Edinburgh at the top of Pool Five with a 28-18 victory at London Irish, who now face likely elimination.
Montpellier claimed a much-needed bonus point in a 47-7 thrashing of Calvisano, which lifted them to second in Pool Three.