The French coach praised his side's exceptional effort while admitting they enjoyed a "slice of luck" as the Basque outfit recorded a memorable victory against the Blaugrana
Lionel Messi and Pedro had put the visitors 2-0 up within 25 minutes, before two from Gonzalo 'Chori' Castro and an injury-time winner from Imanol Agirretxe gave the home side an unexpected three points in a game where Gerard Pique was also sent off for the visitors.
Speaking after the match, Montanier was clearly extremely pleased with his team's performance but refused to get carried away.
"I'm very proud of my squad," the 48-year-old Frenchman was quoted by AS.
"We knew we were going to suffer, we had some difficult moments in the game but we never gave in.
"I hope this win will give us confidence to take a step forward as a team. I hope we see the attitude we showed tonight in the next few games."
Barcelona, who have 18 victories in their 20 league fixtures so far this campaign, have now failed to win in any of their last three trips to Sociedad.
However, despite the fact his side are the first to secure a La Liga win over the Catalans since Real Madrid did last April, Montanier could offer no advice to others wanting to repeat their success.
"There is no recipe to beat Barcelona," he added.
"We won because we our team were compact, hard working and had a slice of luck."
Sociedad are now ninth in the league with 29 points but Barcelona still lead the way on 55.