The hosts hit twice in the space of the minute just shy of the 15 minute mark to gain an early 2-0 lead at the Brentford Community Stadium, through Pontus Jansen and Yoane Wissa.
Despite Saints enjoying a share of possession the decisive third then followed during the second half, Kristoffer Ajer with a mazy run to confirm the defeat.
"We were really poor," reflected Armstrong, "Apologies to the fans who came and supported and stayed to the end and kept signing all the way through. It must have been a hard watch.
"The first 15 minutes we created a good foothold in the game and created chances. We felt comfortable in possession and the problem was we don't score; they went up the pitch and do.
"It's a tough one. We always work hard but now we need something more and we need to win games. Our form has been very perform recently and everyone knows it.
"Everyone would love more consistency within the form and within the games. The good form seems a long time ago now, it was about nine games ago."
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