Getafe heaped more misery on Espanyol by inflicting a 2-0 defeat on the Primera Division's bottom team at the Estadi Cornella-El Prat.
Pedro Leon's early strike set the visitors on their way and Mane put the result beyond doubt with a second goal in stoppage time.
The result left the Barcelona team rooted to last place while Getafe climbed provisionally to seventh in the standings.
Getafe had early sighters through Abdel Barrada and Angel Lafita, both of which flew wide of Cristian Alvarez's goal.
But when they did get a shot on target, they went 1-0 up - Leon's left-footed strike finding the bottom-right corner in the 17th minute.
Espanyol, who headed into the game having won only twice in 12 games in La Liga this term, looked for an immediate response as Wakaso Mubarak unleashed fierce efforts from outside the box. But the first sailed over the bar and the second was saved by Getafe goalkeeper Miguel Moya.
The visitors went close to extending their advantage before the interval, Alvarez doing well to parry Xavi Torres's long-range blast away to safety.
The second half was a scrappy affair with chances at a premium.
Alvarez had to be alert to tip a Leon free-kick over the bar four minutes after the restart, but other than that neither goalkeeper was particularly tested.
Espanyol did spend a large chunk of the second period on the front foot, but lacked cutting edge.
Samuele Longo twice fired wide for the home side and saw a header caught by Moya, while Joan Verdu and Wakaso lashed over the bar and a shot from substitute Christian Stuani was comfortably kept out by Moya.
Getafe had offered little as an attacking force after the interval but showed Espanyol how it was done in front of goal at the end, Mane's left-footed finish into the bottom-left corner from Diego Castro's pass sealing matters.