Daryl Powell’s depleted side took an early 4-0 lead at Halliwell Jones Stadium on Thursday and then quickly created another glorious chance when McShane ran around Liam Watts on the last tackle close to the hosts’ goalline.
A gap opened up in the 11th minute, but, unusually, the Castleford star spilled the ball with the line begging.
Instead, Warrington built up a 16-4 interval lead and the visitors – without seven first-team regulars – could not claw back the deficit, eventually losing 24-10 against their near full-strength opponents.
“It was a tough effort from the lads,” said McShane.
“We don’t really talk about being down on troops – it has been tough – but the people coming in are having a dig.
“I think we were probably in it, but the last try in the second half was a bit of a dampener for us.
“But then if I take that ball off Wattsy and put us 10-0 up I think it could be a different game.
“It was just poor skill by me there. I feel like I’ve let the boys down, but hopefully I can make up for it in the coming weeks.
“It’s something we’ll learn from and build on. We showed a lot of character and you know what people are made of with performances like that.”
Tireless prop Watts was superb for Castleford, who hope to have England forwards Oli Holmes and Adam Milner back for next Sunday’s visit from Salford Red Devils.
McShane admitted: “I think he’s our best player by a mile.
“It showed in pre-season what sort of year he was going to have and he’s been outstanding
“People go on about us and having people injured, but I think Warrington played great.
“Their completion rate was high and they stuck to their plan.
“They bounced back after a tough loss (in Perpignan) and hopefully we can do the same,” he added.
Salford, who visit Catalans this evening, have won three of their opening five games including wins on the road at Hull KR and Huddersfield Giants, but lost versus St Helens last week.
McShane, 29, added: “They are doing well and playing well even if they have had a few results go against them.
“They’re moving the ball well, but we’re just looking forward to getting back out there especially being back at home.
“If we get a few troops back it will be a bonus, but if not the lads are ready to rip in for each other again.”
Powell brought winger James Clare off at half-time after Castleford’s right edge was exposed three times in quick succession.
The coach said: “I thought we were pretty good, to be honest.
“The opportunities we got in good attacking positions and put down hurt us – there was three – and our right edge was poor defensively in the first half.
“I took James Clare off because I don’t think his decision-making was good enough and we should have stopped some of their tries.
“But I thought we were fantastic in terms of effort and spirit, I’m proud of them.”