It was the power of the Saints centres, Kevin Iro and Paul Newlove, that did much of the damage to a Castleford side with a run of four wins behind it, but this was a highly convincing display from the Super League leaders.
Coming off the back of a defeat at Wakefield in which their coach, Ellery Hanley, felt they were beaten for enthusiasm, there was nothing wrong with Saints' desire last night.
It helps, of course, to be able to bring an individual talent like Iro back into the side. After only three minutes, he dummied to Smith, burst through and then picked up the same player in support on the inside for the first try, converted by Sean Long.
Castleford had two wonderful opportunities to hit back, first through Aaron Raper's grubber kick and then Dean Sampson's storming run but both were squandered.
There was soon a price to pay for those omissions and again it was the combination of Iro and Smith that extracted it.
Vila Matautia's run began the thrust and Iro's overhead pass allowed Smith to go through Darren Rogers for the try.
Iro appeared to have sent Newlove over for another only for his fellow centre to be held up over the line. Further points were not long delayed, Tommy Martyn and Paul Atcheson throwing the ball around for Long to sneak over.
The first real sign Cas might get back into the game came when Atcheson was sin-binned for deliberate offside. Almost immediately, James Pickering made the breakthrough, blasting through the defence to release Rogers. Brad Davis could not convert that nor kick an earlier penalty and he was guilty of a different miscalculation when he was sin-binned for interfering at the play-the-ball.
Four minutes into the second half and with Davis still off the field, Smith's hat-trick try was the most spectacular so far. It came from deep in defence, Kieron Cunningham taking Dale Fritz's dangerous kick above his head to send Fereti Tuilagi on an 80-yard sprint which only required Smith to go the last few yards.
Castleford's reply was almost as good, Danny Orr taking Davis' chip-kick and feeding it back to his half-back partner for a virtuoso effort.
Time for another demonstration of Saints' firepower, with Newlove scoring two magnificent individual tries before Adrian Voles' flick-on produced a riposte by Richard Gay.
That was as close as they could get, Martyn rounding it off with a late drop goal.
"The players switched themselves on for this game," Hanley said. "The battle was won from the first minute. You know whether they are ready for the game and they were tonight."
Castleford: Flowers; Gay, Eager, Vowles, Rogers; Orr, Davies; Sykes, Raper, Sampson, Tallec, Fritz, Harland. Substitutes used: Pickering, Tonks, Heppi, Ellison.
St Helens: Atcheson; Stewart, Iro, Newlove, Smith; Martyn, Long; O'Neill, Cunningham, Matautia, Joynt, Perelini, Sculthorpe. Substitutes used: Tuilagi, Edmondson, Vollens, Jonkers.
Referee: S Cummings (Widnes).Reuse content