However, McFadden refused to blame his No7 for two forward passes and was satisfied with his attacking intent when a desperate ankle tap from Billy Slater saw Johnson lose possession as he looked headed for the try line.
"There were other people involved in that who were a little bit off and I thought it was one of Shaun's stronger performances," McFadden said.
"He got himself in the clear, he ran the ball tonight. It was a real positive sign for him, and had the rest of the team done what they were supposed to do and held the ball, it could have been a different result."
After absorbing plenty of pressure, the Storm opened the scoring when right wing Mahe Fonua cleaned up a loose pass from Will Chambers to dive over out wide. Cameron Smith then kicked the first of his five goals.
Eleven minutes later, the Storm broke through again, with left wing Marika Koroibete brushing past Jonathan Wright and Hurrell to race in.
Manu Vatuvei lifted the Warriors' spirits three minutes before halftime when he grounded the ball on the chalk just inside the touch line, despite the attention of three defenders, but Johnson was unable to convert.
Melbourne extended their lead seven minutes after the resumption with Cooper Cronk and Slater working a chip and regather before Cronk, Kevin Proctor and Fonua combined to send Chambers over.
The Warriors earned a repeat set in the lead up to Nathan Friend ducking over for a try from dummy-half with a quarter remaining, but they were quickly put on the back foot when Koroibete broke downfield before Slater put Tim Glasby in for their reply.
With the clock winding down, Sebastine Ikahihifo managed to wrestle his way over to keep hopes of a late rally alive, but the Storm again kicked clear when Koroibete dived in for the match-winner.
With two wins and three losses behind them, McFadden was confident the Warriors could regroup ahead of Saturday's home game against Wests Tigers.
"The players know where we went wrong but they all believe in what we are trying to do and it's not that far away. We know it doesn't take too much more to really start to click."
Storm 30 (Mahe Fonua, Marika Koroibete 2, Will Chambers, Tim Glasby tries; Cameron Smith 5 cons)
Warriors 14 (Manu Vatuvei, Nathan Friend, Sebastine Ikahihifo tries; Johnson 1 con)