Asked what went wrong in Armenia, the former Jamaica manager said “almost everything”.
“We were not as solid defending like we normally are, we lost a lot of duels, in possession we made lots of mistakes and lost the ball in tough areas.
“Armenia can be quick on the counter and they have good individuals with good individual skills, and they deservedly won.
“There are a lot more negatives than positives, that is for sure. We are hugely disappointed.”
Trailing 1-0 at half-time, Hallgrimsson introduced Adam Idah and Kasey McAteer off the bench in place of Jack Taylor and Chiedozie Ogbene.
“We wanted to change it tactically, we thought we needed a goal early so we wanted two strikers and that was successful three days ago so that was one of the reasons we did this change,” he explained.
“Also [we wanted] fresh legs, but the substitutions are on me, of course.”
On failing to potentially involve star striker Ferguson sufficiently, the Republic boss added: “We didn’t create a lot of chances. It is not about him or how we can involve him. The whole team were not on it and it was Armenia’s day, not ours.”
Captain Nathan Collins also told RTE the better team won and reflected on his team’s shortcomings.
“I probably do think they were the better team, which is nowhere near where our standards should be,” said the defender.
“We didn’t create enough. It probably wasn’t defensively strong enough and overall, just wasn’t a good enough performance.
“We have to beat Portugal, that’s the be all and end all. We have to go there and get a result and that’s all I can say.”