The Tigers travel to Salford Red Devils on Thursday night knowing that a defeat will bring the curtain down on their 2019 campaign.
Victory will send Castleford into the Preliminary Final, where they will face the loser of Friday night’s contest between St Helens and Wigan Warriors at the Totally Wicked Stadium.
The Tigers’ fifth-placed finish has given them the most difficult route to the Grand Final at Old Trafford but Powell feels his side can use it as motivation.
“There is a motivation because it would be something special, so from that point of view we have grabbed hold of that a little bit,” he said.
“It has been done from fifth before so it is certainly not impossible.
“It is very difficult. You are away from home in three games if you get to the Grand Final and we have just got through the first hurdle.
“We have got an opportunity now to get through the second.
“We are probably the biggest underdogs and we have got a lot of players missing.”
Castleford were without captain Michael Shenton, 2017 Man of Steel Luke Gale and domineering forward Mike McMeeken for last week’s 14-12 triumph at Warrington Wolves.
Meanwhile, Salford were beaten 18-12 by Wigan at the DW Stadium last Friday, to set up Thursday’s clash with the Tigers.
Powell admits that his players have been in knockout mode since their home win over Hull.
Defeat against the Black and Whites would have ended the Tigers season and although they were beaten a week later by Wigan, Hull were unable to take Castleford’s play-off spot as they lost at home to St Helens.
Powell said: “It’s the end of the season if you lose and we have been aware of that for a few weeks now. We beat Hull and that gave us the opportunity to be where we are now.
“But then the week after we lost to Wigan and could have been out that week.
“And we could have been out last week so it’s been three weeks straight were we have know, ‘this is it, we have to win.’
“And two out of those three weeks it has gone our way and I think we are in a good place.”
Salford finished the regular season in third place, four points ahead of Castleford.
The sides have met twice in Super League this campaign, claiming a win each.
“They are a good side but nobody is infallible and unbeatable,” Powell said.
“We are confident that we can go and win, we know it is going to be difficult we have just got to play well.
“We need every player to play well and we need a massive lead, like we got last week, from our senior players.
“And I think we are good enough do it.”