Twelve-point leads over Salford mean little to Castleford who twice lost that advantage when they were beaten at home last month and were overhauled again at The Willows to slip closer to relegation.
The handling skills of Gavin Clinch in the second half steered Salford to a victory which puts a six-point gap between them and a Tigers side that looks increasingly doomed, although a very different outcome was on the cards when Cas, helped by the long-range kicking of their returning old boy Brad Davis, swept into their early lead.
Paul Mellor bounced out of Joel Caine's tackle for their first try after five minutes and Andy Lynch took Jon Hepworth's pass to go over after 17, with Wayne Godwin converting on both occasions.
Salford had been guilty of over-elaborating when a glance at Castleford's team sheet should have shown them that they would tire in the forwards if forced to work hard.
The Reds started to repair the damage when Clinch gave Andy Coley the chance to power his way over, and they were level after 33 minutes when Cliff Beverley's well-timed pass sent Anthony Stewart away and Malcolm Alker was in support to score.
Godwin's penalty edged Cas back in front by the break, but the second half belonged to Salford. Clinch went wriggling through to supply the ball to Chris Charles for the converted try that gave them the edge once more, although it took a wonderful piece of defensive work to preserve it.
Mellor was storming down the left touchline for the try that could have put Cas back in the lead, only for Stewart to come across from the opposite wing and make a candidate for tackle of the season.
"It probably cemented the result for us and it was an outstanding effort from him,'' said his coach, Karl Harrison.
Clinch got another classic short pass away to put Mark Shipway over and Salford were virtually safe, Alker getting his second from Karl Fitzpatrick's dazzling break seven minutes from time.
"It's a great result for us," said a relieved Harrison. "I'm just so pleased for the guys in there. We haven't got the most talented team in Super League by a country mile, but they work very hard."
Castleford coach Gary Mercer remained calm: "I'm not going to panic," he said.
Salford: Flowers, Caine, Littler, McGuinness, Stewart, Beverley, Clinch, Baynes, Alker, Highton, Coley, Rutgerson, Charles. Substitutes used: Haggerty, Fitzpatrick, Johnson, Shipway.
Castleford: Hepworth, Pryce, Tony, Gibson, Mellor, Davis, Robinson, Jackson, Godwin, Lynch, M Smith, Ryan, Hudson. Substitutes used: B. Smith, Clayton, Saxton, Ripley.
Referee: K Kirkpatrick (Warrington)
- More about:
- North West England