Banega converted his shot at the second time of asking to put Sevilla ahead in the 13th minute on a bitterly cold and wet evening at the Jose Zorrilla stadium.
Nolito missed a glorious chance to double his side's lead later in a first half which was high on intensity but short on goalmouth action, firing into Masip's hands when unmarked in the box.
Earlier, Karim Benzema scored his sixth goal in five games to help Real Madrid beat high-flying Real Sociedad 3-1 as Gareth Bale came on as a substitute to a screech of whistles at the Santiago Bernabeu.
Bale, only recently fit again after a calf injury, was named on the bench following his controversial outing with Wales last week, when he celebrated victory behind a flag that read: "Wales. Golf. Madrid. In that order."
Barca on top
Meanwhile Barcelona extended their stay at the top with a 2-1 win over bottom-club Leganes.
Youssef En Nesyri gave Leganes an early lead in the 11th minute which was cancelled out by Luis Suarez in the 52nd and the Catalans required a late winner from Arturo Vidal in the 78th minute.
Atletico Madrid however lost ground at the top. They were held to a 1-1 draw away at Granada and now sit three points behind the leading pair, having played one game more.
The outcome of the rescheduled El Clasico at Camp Nou on December 18 will now have a major say in deciding the La Liga.