Almeria pressed the self-destruct button as Osasuna finally registered their first league win of the season.
It started well for the visitors when Alvaro Negredo gave them a sixth-minute lead from the penalty spot but they then imploded.
Guilherme was sent-off four minutes later for a reckless challenge and the 10 men conceded an equalizer when Walter Pandiani headed home after a quarter of an hour.
Almeria then gifted the Pamplona-based hosts the edge when Hernan Pellerano nodded into his own net with 19 minutes remaining.
Krisztian Vadocz added a third for Osasuna in the final minute.
Osasuna went into the contest as the only side in the Primera Liga without a win this season having drawn five and lost six of their opening 11 fixtures.
They looked to be facing more disappointment when Negredo slotted home from the spot after Cesar Azpilicueta fouled Hernan Pellerano inside the area with the pair grappling to reach Jose Ortiz's outswinging corner.
Azpilicueta was a pivotal figure in the opening stages and it was he who was on the receiving end of a wild elbow from Guilherme shortly afterwards, a challenge which gave the referee no option but to issue a red card.
It started to unravel for Almeria very quickly as Osasuna equalised after 15 minutes, Pandiani heading in Massoud Shojaei's left-wing cross from 12 yards.
Pablo Piatti threatened to restore Almeria's advantage after 27 minutes but dragged his shot from the edge of the area past the right-hand post.
Javier Portillo, a 40th-minute replacement for the injured Pandiani, came close within two minutes of his introduction, shooting narrowly wide from inside the area.
The 10 men of Almeria were still offering a threat on the break and Juanito headed a corner wide approaching half-time.
It was Osasuna who went into the break cursing their luck, however, as only a fine save from Diego Alves denied Juanfran Torres a goal in first-half injury-time.
Osasuna also started the second half on the front foot as Almeria tired.
Francisco Punal shot wide after 49 minutes while Javad Nekounam ought to have done better than head Massoud Shojaei's corner over the bar from inside the six-yard box.
The pressure continued to mount and Portillo came even closer with a 25-yard drive which struck the post with Alves beaten.
The third goal of the contest finally came in bizarre circumstances with Pellerano nodding past a stranded Alves after 71 minutes.
Nekounam was denied by the Almeria keeper after 79 minutes but Osasuna did add to their tally when substitute Vadocz, following good work from Ludovic Delporte, slotted into the bottom right-hand corner deep into stoppage-time.
