Leeds Rhinos became the first side to defeat St Helens in 2018 after picking up a 20-28 victory.
The two sides were level at the break, with Ben Barba and Adam Swift’s tries being cancelled out by scores from Richie Myler and Anthony Mullally.
But Ash Handley scored twice in the second-half, and despite Barba bagging a second, Matt Parcell pinched a try to earn the win.
St Helens: Barba; Swift, Makinson, Percival, Grace; Lomax, Richardson; Amor, Roby, Thompson, Peyroux, Taia, Wilkin. Subs: Fages, McCarthy-Scarsbrook, Douglas, Lees.
Leeds: Golding; Briscoe, Watkins, Handley, Hall; Moon, Myler; Mullally, Parcell, Singleton, Jones-Buchanan, Ablett, Delaney. Subs: Walker, Smith, Oledzki, Walters.