First-half goals from Jaroslav Plasil and Masoud Shojaei inflicted a sixth straight defeat on the Soria-based outfit, leaving them at the foot of the Primera Liga table in the wake of Espanyol's shock victory over leaders Barcelona in Saturday's Catalan derby at the Nou Camp.
The result stretches Osasuna's unbeaten run to five matches and keeps them out of the drop zone, despite the pressure applied by Espanyol's result and Real Mallorca beating Racing Santander.
The Pamplona-based side came into the game knowing anything other than a victory would put a dent in their survival prospects.
And they were clearly determined to take the game by the scruff of the neck, snatching the lead with their very first attack inside two minutes.
Walter Pandiani slipped a pass between two defenders for Plasil to advance on goal, and the Czech international made full use of the opportunity by threading the ball through the legs of Juanra and firing an arrowed shot into the bottom corner with his left foot from 18 yards.
It was a hammer blow to Sergio Kresic and his players, and although Numancia looked to respond quickly the hosts could have doubled their lead on 15 minutes.
Cesar Cruchaga climbed above the defence to get a clean head on the ball four yards from goal following a Francisco Punal free-kick but he could only direct his effort inches wide of the far post.
Txomin Nagore then came close for the visitors moments later when he thrashed a volley at goal from distance, but the ball sped off the turf beyond Roberto's far post as Numancia started to dominate possession in their search for an equaliser.
Osasuna seemed quite happy to soak up the pressure and it proved to be a cunning ploy when they grabbed a second goal from a swift counter-attack on 36 minutes.
Juanfran made full use of space down the right flank to penetrate deep into Numancia territory, and his low diagonal cross towards the six-yard box was poked into the far corner by the right boot of Masoud.
It was a classic sucker punch but Numancia could have few complaints.
Jose Antonio Camacho's men were looking the more accomplished outfit and appeared to be in control of proceedings, so they were probably good value for their two-goal advantage going into the interval.
The second half continued in much the same vein with chances few and far between for the visitors.
They did, however, hit a post when Antonio Guayre found a yard of space inside the 18-yard box and fired a right-footed effort against the left upright on 79 minutes.
However, the lion's share of the openings came Osasuna's way and they might have increased their lead further had Juan Pablo Colinas not been equal to shots from Plasil, Javad Nekounam and substitute Antonio Idalgo.