It was the Saints' second successive defeat following their win over Premier League champions Manchester City, and it leaves them hovering just above the relegation zone.
Captain Adam Lallana was forced off following a clash of heads with counterpart Clint Hill, and Pochettino has other injury concerns ahead of their visit to Norwich next Saturday.
"Adam Lallana had a knock after coming together with another player on the neck and that is why he couldn't continue," said the Saints boss.
"Danny Fox had a knock on (his) quadriceps, which led to him being substituted as well. We do not know how serious it is. In the next couple of days we will do the necessary analysis.
"We have to accept that because we made some mistakes," Pochettino added.
"We've tried very hard. We've put in a great effort to try and get a different kind of result.
"But because of some mistakes we have made and their goalkeeper's intervention a couple of times we didn't get a positive result."