Tuesday night’s 1-0 defeat to Group D leaders Serbia in Dublin, coupled with Wales’ 2-0 win in Moldova, sees Martin O’Neill’s men slip to third in the table, with just two games remaining.
“We know it was a big turning point in the group, but it’s still in our hands,” Long told RTÉ Sport.
“We’ve got to do it the hard way now – three points against Moldova and go to Wales and have to win, and that’s what we plan to do.”
Serbia now enjoy a four-point lead over Wales, who have leap-frogged Ireland into second place, with Ireland a point behind Chris Coleman’s side.
Ireland face two must-wins games against Moldova in Dublin on 6 October, and in Cardiff against Wales on 9 October, and will need a maximums six points if they are to have a chance of reaching the play-offs.
On 6 October, Wales travel to Georgia, who have yet to win a game, meaning Cardiff should be a mouth-watering showdown for second place.
While it was Ireland’s first defeat in the group, the loss means they have now picked up just three points from their last four qualifying fixtures.
Three wins from their opening four fixtures had put Ireland in a position of strength, and challenging for automatic qualification, but that is now a pipedream.
“We’ve been there before. Just remember the Italy game in the Euros, when we’re asked the question we normally stand up…. but we can still do it,” added Long.
Former Manchester City defender Aleksander Kolarov scored the only goal of the game for Serbia in the 55th minute, and the visitors held on despite Nikola Maksimovic’s 68th minute red card.
Ireland racked up 17 shots on the night, to Serbia’s eight, but couldn’t find a way through.
“I don’t think we did a whole lot wrong, I thought we played really well,” added Long.
“It’s weird; we didn’t really perform against Georgia and came away with a point, we did well tonight and came away with nothing.
“It’s frustrating, but we’ll learn from our mistakes. Moldova at home, hopefully we can get a win there and then it’s all to play for against Wales.”
Long said that manager O’Neill was “proud” of the team’s performance, but admitted that one point six from their games with Georgia and Servia wasn’t good enough.
“The chances just didn’t come our way I suppose. I thought we played really well, limited them,” he said.
“It was a great finish from Kolarov but I think they’ll feel over the moon to come away with a win because I think we deserved a lot more from the game, a few goals would be nice. I don’t think we are doing a whole lot wrong.
“Hopefully, our luck will turn a little bit in the next few games and hopefully I’ll go back to the club, get a few more minutes on the pitch and bring that form in.”