He cited a foul on defender Nathaniel Clyne and an offside decision which was not given during the build-up.
The goal put the Magpies ahead after Moussa Sissoko had cancelled out Morgan Schneiderlin's early opener. Saints levelled through Rickie Lambert but a Yohan Cabaye penalty and Jos Hooiveld's own goal put the game beyond them.
Pochettino said: "We are very sad about the result, especially taking into account how well we started.
"But especially after we got the first goal, we couldn't really control the game as we should have.
"We went in at the end of the first half losing the game and for their second goal, it is clear that there was a foul on Clyne, and then that was followed up by an offside. That is clear on the images.
"It's not a complaint, but these are details that had an influence on the end-result of the match."