Bilbao beat Osasuna to ease pressure on Bielsa
Athletic's new Argentine coach Marcelo Bielsa had been under pressure after the Basque club took only two points from their opening five games but a second consecutive win lifts them to 11th on eight points from seven matches.
Spain Under-21 international Muniain (pictured) put the home side ahead on the half hour at their imposing San Mames stadium, before Gabilondo and Martinez made it 3-0 before the break.
Osasuna's Iran midfielder Javad Nekounam pulled a goal back from the penalty spot in the first minute of second-half stoppage-time after Martinez handled the ball in the area.
The Pamplona-based club finished the match a man down after their Ivory Coast-born midfielder Roland Lamah earned two yellow cards in the space of seven second-half minutes.
The second came with around 20 minutes left after he appeared to catch Muniain on the side of the head with a flailing arm.
In weekend action, La Liga top scorer Lionel Messi netted his ninth and 10th goals of the campaign in a 3-0 win for Barcelona at home to Racing Santander on Saturday.
The champions were joined at the top on 17 points by surprise package Levante. The tiny Valencia-based club extended their remarkable early-season run with a 3-0 win at home to 10-man Malaga on Sunday.
The pair have a one-point advantage over third-placed Real Madrid, who thumped visiting Real Betis 4-1 on Saturday thanks to a third hat-trick in two weeks from Messi's Argentina team-mate Gonzalo Higuain.