Paasi got Saints off the mark courtesy of some fine work from Owen Dagnall, with Murphy touching down for his first soon after when Cross and Hastings combined to send him over in the corner.
Murphy had his second eight minutes later, this time when Tristan Sailor offloaded to tee him up for another dash to the line.
If that was good, then Saints’ fourth try of the evening was even better – a high kick into the Toulouse 10 was met by Sailor, who put in an audacious offload to Klemmer who coasted over with ease.
Cross bagged a try of his own, Saints prospering from a six-again with Jake Wingfield putting in a short pass in the build-up.
Toulouse had a better go of things after the break and finally made their pressure count as Laguerre went in for their first score of the night.
They then continued to keep the visitors pegged in their own half, eventually working the ball wide to Polselli to score in the corner, while Dupree reduced the deficit further.
However, a late tackle on Klemmer in the closing stages allowed former Man of Steel Hastings to kick over a late penalty – which proved to be Saints’ only points of the second half.
St Helens have won four of their first five Super League matches in 2026 and are two points behind leaders Wigan, while Toulouse slipped to a third defeat in five outings.