La Real were at it from the start, pushing Benfica deep into their own half.
They were rewarded for their efforts in the opening 10 minutes when Mikel Merino pounced on an exasperated shot to head home to give the home side the lead.
Things quickly went from bad to worse for Benfica as Sociedad captain Mikel Oyarzabal pounced on a disastrous game from behind to fire the LaLiga side two ahead just five minutes later.
The tie was all but dead as the clock ticked down after 20 minutes when Ander Barrenetxea went inside and fired a raspy shot into the top corner to put Sociedad three up with the snap of a finger.
Benfica were spared the blushes before the 30th minute, however, as Brais Méndez sent a free-kick off the post after Nicolás Otamendi had fouled a Sociedad player in the box.
Rafa Silva gave Benfica a lifeline shortly after the restart when he cut the visitors’ lead to two with most of the second half still to play.
Benfica posed little threat after Silva’s strike and struggled to get back into the game, while Sociedad slowed the pace of the game to a crawl.
An impressive win saw Real Sociedad move to the top of Group D.
Benfica Player Rating
Trubin – 5.7
Silva – 6.5
Otamendi – 6.6
Morato – 6.9
Neves – 7.6
Luis – 4.9
Mario – 6.5
Silva -7.0
Di Maria – 6.8
Cabral – 6.8