Nile Ranger scored a goal, Yaser Kasim netted the other and produced a man-of-the-match performance in Town's backs-to-the-wall 2-1 win over out-of-sorts Posh, who have now suffered four straight League One losses.
Substitute Nathaniel Knight-Percival scored his first Peterborough goal with 12 minutes of normal time remaining. He chested the ball down before rifling a 20-yarder into the back of the net off the underside of the crossbar. But that was all Posh could manage.
"Things just aren't happening for us at the moment, but we put in a terrific shift and if we continue to play like that I'll be more than pleased," said Ferguson.
Posh were not helped by Tomlin's dismissal - for a second time this season - after collecting two yellow cards in the space of 20 second-half minutes.
He received his second caution after shoving Kasim to the floor.
It was the seventh red card of Tomlin's career and Ferguson was in no mood to offer sympathy to a player who was upset he was not allowed to join Celtic in August.
"If Lee thinks that by behaving like this he will get a move away from the club he's sadly mistaken," Ferguson said.
"In fact, I will go the other way. We won't simply wash our hands of him, we will make sure he doesn't go anywhere.
"He now owes me and his team-mates massively. It showed a serious lack of judgement after he'd already been booked.
"I asked him what he was thinking, but I suspect even he doesn't know. He will punished, but what that punishment will be I don't know yet."
Shortly after Tomlin got his marching orders County Ground stewards had to intervene in a 20-man touchline fracas which broke out in front of the dugouts and culminated in Posh goalkeeping coach Jimmy Walker being sent to the stand.