They won for the first time in four games by defeating Salford Red Devils, despite being without a raft of key personnel - and no recognised half-back.
Scrum-half Luke Gale strained a hamstring on Thursday, stand-off Benny Roberts has been sidelined since March and Luke Dorn, on his return from injury, pulled out in the warm-up.
Australian prop Grant Millington played at six but it was McShane, the burly former hooker signed from Wakefield Trinity, who slotted in at scrum-half and took firm control.
“I thought he was exceptional,” said Powell, about the 26-year-old who scored one try and kicked four goals.
“But as soon as we put him there I said ‘if we win, he’ll get man of the match’.
“He’s a composed player and when you play in a different position it brings something else out of you - I’ve experienced that in the past.
“Maybe half-backs aren’t as valuable as they think they are!
“I thought today we recognised where space was really well.
“Credit to the guys, they never gave up; their commitment, effort and attitude was a big plus for us - everyone played well.”
It was a fitting tribute to Roger Millward, the former Castleford, Hull KR and Great Britiain stand-off rated one of the all-time greats, who died earlier this week at the age of 68.
There was a minute’s applause before kick-off as fans at Wheldon Road, close to where he was born, watched a BBC montage of some classic Millward clips on the the big screen.
In an entertaining Cup tie, Castleford, with hard-running second-row Junior Moors also in blistering form, went in at half-time 18-12 and never looked back.
It was the least their efforts deserved; Powell’s side may have been patched up and on a three-game losing run but they were operating just fine and also showed real character to overcome an early setback.
Salford centre Junior Sa’u had crossed after nine minutes, exploiting some weak defence from 40m out.
Thereafter, though, there was little such meekness as Castleford knuckled down and went about grinding Salford down.
They made an immediate response as Joel Monaghan palmed down Ryan Hampshire’s accurate chip for Mike McMeeken to score.
Powell’s side had plenty more pressure but did not add to their score so the visitors went 12-6 ahead when Sa’u dived on Robert Lui’s grubber after a rare attack of their own on 28 minutes, Gareth O’Brien adding his second conversion.
However, the Tigers, who saw ex-England second-row Danny Tickle called up for his debut after Dorn’s late omission, finally got their rewards when they scored twice in as many minutes just before the break.
McShane produced a lovely chip that Solomona palmed down for Webster and then a brilliant handling movement down the other side saw Joel Monaghan send McMeeken in for the big back-row’s second.
McShane converted both and they extended their lead when Solomona scored early in the second period, although video replays clearly showed he never actually got near touching the ball down under pressure.
Lui dummied over at the other end soon after for O’Brien to make it 22-18.
However, McShane twisted over from close range, bumping off Lui when he had no right to score, and he added another conversion.
Ex-Tiger Justin Carney bombed a try in the corner when he dropped Lui’s ball so, when Solomona intercepted Dobson’s pass to race 90m in the 74th minute for his 16th try of the year, the visitors were finished.
The quarter-final draw is tomorrow and Castleford head to Super League’s bottom club Leeds Rhinos for another televised game on Thursday.
Castleford Tigers: Hampshire; Monaghan, Crooks, Webster, Solomona; Millington, McShane; Patrick, Milner, Jewitt, Moors, McMeeken, Massey. Substitutes: Cook, Springer, Hitchcox, Tickle.
Salford Red Devils: O’Brien; Carney, Sa’u, Jones, Vidot; Lui, Dobson; Kopczak, Joseph, G Griffin, Murdoch-Masila, Hauraki, Flanagan. Substitutes: J Walne, A Walne, Krasniqi, Evalds.
Referee: James Child (Dewsbury)