The Australian winger scored a try in each half to give him 19 for the season though his second was served up on a platter for him by his team-mate Chris Atkin – passing to him when already over the try-line.
Salford trailed 14-4 before half-time but they rallied superbly, scoring a crucial try just before the break then blitzing the Super League champions with three tries in 12 minutes after the restart to lead 26-14.
Retiring Salford half-back Kevin Brown was not fit to play but he was afforded a guard of honour from both sets of players and presented with a framed shirt before kick-off.
St Helens took the opportunity to give some of their senior players a break with the end of season play-offs around the corner. Shay Martyn, Jon Bennison and Sam Royle all made their debuts and 12 of the Saints 17 were products of the club’s famed academy system.
And two of those youngsters were soon in the points. Only four minutes had been played when Regan Grace broke dangerously up the wing and he passed inside to Lewis Dodd who in turn fed Bennison and he touched down under the posts. Martyn, son of Saints great Tommy, stepped up to kick the conversion and give the visitors a 6-0 lead.
Salford responded in the 11th minute through Sio. The Australian winger was first to react to a kick to the corner by Tui Lolohea though Morgan Escare was off target with his conversion attempt.
Saints extended their lead thanks to another flash of brilliance from Grace. The Welsh winger cut infield dangerously and he kicked ahead for Jonny Lomax to ground the bouncing ball. Martyn added the conversion and followed it with a penalty goal two minutes before half-time after Salford were penalised for obstruction.
Seconds before half-time, Salford cut the deficit to just four points when former Saints centre Matt Costello slid over on the right edge after some slick approach play. Atkin, making his 200th career appearance, took over the kicking responsibility and landed the conversion from off the touchline to make it 14-10 at the break.
The home side needed only three minutes of the second half to take the lead for the first time in the game. Andy Ackers broke dangerously and the supporting Ellis Robson fed Atkin who crashed over for a try he also converted.
Robson, having set up a try moments earlier, scored himself soon after as he charged through from close range. Krisnan Inu’s conversion attempt hit the post and Salford’s lead remained six points.
Salford claimed a third try 12 minutes in when a break from Rhys Williams split the Saints defence wide open and Atkins could have scored easily but passed to Sio so he could register his second try of the night. Inu added the conversion to make it 26-14.
Saints barely troubled Salford in the final quarter and indeed it was the home side that seemed more likely to add further points.