It needed an 86th-minute own goal from former Forest man Jamaal Lascelles to secure the Reds’ third-straight Championship win, and leave Rafael Benitez’s men hugely frustrated.
Matt Ritchie gave Newcastle the lead in between two missed penalties for the home side – incidents which also saw Jonjo Shelvey and Paul Dummett red carded, both for fouls on Henri Lansbury.
But firstly Nicklas Bendtner and then Lansbury were denied by the heroics of another former Forest man, keeper Karl Darlow.
Bendtner pulled Forest level seven minutes into the second half but they had to wait until the final few minutes to secure all three points.
“We had to be patient in the second half to push higher, to get a lot of crosses in and create opportunities to score. We had to respect the plan but we did that and we got the goal at the end,” said Montanier.
“It was difficult for me to see whether they were clear penalties, but we cannot change the referee’s decision. We were on a downer after missing the two penalties, but I told the players to be clear in their minds – we had 45 minutes still to win the game and we knew we only needed a few seconds to score a goal.
“We had to forget the penalties and be patient – and we were. They had nine men and we had to move the ball. We had to deliver crosses and get bodies in the box.
“We needed to be accurate with the crosses. But the most important thing is that we got the two goals and the three points.”
Magpies boss Benitez was upset with referee Steve Martin, although there seemed to be little to question with either of the red card decisions, with Shelvey sent off for lashing out at Lansbury and Drummett for bringing down the midfielder when he was through on goal.
“It is very difficult to understand what happened. We had a penalty that was not given, I thought their first goal was offside,” said Benitez.
“We had two penalties given against us, two red cards and I hope he (Henri Lansbury) is proud of his reaction for the first one.
“I have not spoken to the referee. But I think we did really well, considering the first goal was offside. We did what we had to do. We tried to play on the counter attack, but that was always going to be difficult when we had nine men for 45 minutes.”