Turner, the ex-Salford and Hull FC centre, switched to stand-off to replace Travis Burns and crossed for the opening touchdown of the second half after his side led 16-4 at the break.
Mark Percival also scored two tries for St Helens, who handled the difficult conditions better than the Giants.
Huddersfield, who have finished in the top three for the last three seasons, handed debuts to Ryan Hinchcliffe, Sam Rapira and Daniel Smith but were missing injured quartet Joe Wardle, Craig Huby, Kyle Wood and Luke Robinson.
Huddersfield stunned Saints with an opening day 40-4 romp at Langtree Park in 2013 and made a bright start with a long-range Jamie Ellis kick just rolling over the dead-ball line, to the Saints relief.
But it was Saints who opened the scoring after seven minutes on their first real attack.
A teasing Jon Wilkin kick was pounced on by Mark Percival but Luke Walsh could not land the touchline conversion.
Hinchcliffe did his best to get the Giants back on level terms with a scuttling burst from dummy half but was held short before Adam Swift was forced to make a timely interception.
Huddersfield kept up the pressure and were rewarded with a try in the corner from Aaron Murphy after slick handling from a scrum after 13 minutes.
A Danny Brough 40-20 kept Saints on the back foot but the home side notched their second try, Atelea Vea dribbling the ball over the line from Walsh’s kick to open up a 10-4 lead.
Saints could never relax, with Jamie Ellis going close after more Giants enterprise.
Again Huddersfield were hit on the counter-attack, with Percival cutting inside from Owens’s pass for his second try and Walsh adding the conversion.
The Giants almost bagged a touchdown but Grix’s kick rolled over the line with Murphy ready to pounce to leave Saints ahead 16-4 at the interval.
Huddersfield suffered a blow when Brough failed to reappear after the break and they almost fell further behind, but Leroy Cudjoe came to the rescue when Wilkin chased a Walsh kick.
Turner forced his way over for his milestone try, with Walsh adding the goal to make it 22-4.
Ukuma Ta’ai pulled a try back for Huddersfield before James Roby went off injured but Saints replied when Louie McCarthy-Scarsbrook tapped back a Walsh kick for Luke Thompson to cross.
Huddersfield’s injury woes continued with Grix going off with a shoulder injury but they never gave up and deserved Jake Connor’s try from an Ellis kick. Walsh struck a penalty to make it five goals from six attempts.
St Helens: Owens, Makinson, Peyroux, Percival, Swift, Turner, Walsh, Amor, Roby, Tasi, Wilkin, Vea, McCarthy-Scarsbrook. Substitutes: Walmsley, Richards, Savelio, Thompson.
Huddersfield: Grix, McGillvary, Cudjoe, Connor, Murphy, Brough, Ellis, Rapira, Hinchcliffe, Crabtree, Ta’ai, Lawrence, Patrick. Substitutes: Smith, J. Johnson, Leeming, Roberts.
Referee: R Hicks (RFL).