French striker Jeremy Perbet fired Villarreal to a 22nd minute lead on Saturday before Javier Aquino doubled the advantage only eight minutes later.
Substitute Ikechukwu Uche scored the third goal for Villarreal on 75 minutes as Osasuna failed to convert a large possession advantage into chances on goal.
The win provisionally lifted Villarreal to top of the league on nine points with four teams on six points set to play on Sunday.
A solitary strike from defender Marc Valiente was enough to secure Real Valladolid a 1-0 win against Getafe.
Valiente's 47th-minute winner meant Valladolid picked up their first win of the season after starting with two losses.
Celta de Vigo drew 1-1 with Granada despite dominating possession and chances on goal.
Rafinha got Celta off to a perfect start with a goal on 29 minutes but Granada managed to equalise through Piti in the 62nd minute.
It was a disappointing result for Celta, who dominated possession 65 per cent to 35 and fired in 17 shots to Granada's three efforts on goal.
