In the first 45 minutes, Real Madrid were limited by a serious defensive display by Osasuna's back five, and an insistence on constantly looking for Vinicius Jr as their main attacking outlet.
Jon Moncayola hit the post for Osasuna four minutes after the restart after good work from Chimy Avila, while at the other end, Karim Benzema smacked a curling shot against the woodwork.
Real Madrid continued to attack down the wings in the second half, but every ball they sent into the Osasuna penalty area was repelled by the visitors' rock-solid defense, and although Marcelo and Casemiro both went close in the final minutes, Osasuna claimed a point to show their current sixth place is no fluke.
Real Sociedad will return to the top if they take a point from their visit to Celta Vigo on Thursday, reports Xinhua.
FC Barcelona suffered another defeat as they went down 1-0 to Rayo Vallecano on Wednesday night.
Radamel Falcao's 30th-minute goal separated the two sides as Barca tried but failed to find an equalizer in the second half, with Memphis Depay seeing a 71st-minute penalty well saved by Rayo keeper Stole Dimitrievski, who also claimed the rebound.
Sergio Aguero, Gavi, and Luuk de Jong all went close for Barca, but KRonald oeman's side failed to find an equalizer and have not won any of their last five away games this season.
Sevilla thought that Lucas Ocampos had scored a late winner to overturn Antonio Sanchez's first-half opener for Real Mallorca.
However, his strike was ruled offside and the two teams shared the points with Erik Lamela's powerful shot leveling for Sevilla 15 minutes from time.
Real Betis are also right in the battle for the top four after thrashing Valencia 4-1. Borja Iglesias put Betis 2-0 ahead, and although Gabriel Paulista's 39th-minute goal gave Valencia brief hope, second-half strikes from German Pezzella and Juanmi rounded off a comfortable win for Betis.
Valencia have taken just three points from their last seven matches, and with games against Villarreal, Atletico Madrid, and Real Sociedad on the horizon, Jose Bordalas needs to see a rapid improvement.
Atletico and Real Sociedad both play on Thursday, while Tuesday saw Espanyol and Athletic Bilbao draw 1-1, while Alaves beat Elche 1-0 and Villarreal and Cadiz drew 3-3.