Hull FC were on a high after winning the Challenge Cup but their League Leaders Shield hopes took a knock from St Helens.
St Helens brought Challenge Cup winners Hull FC back down to earth with a 31-10 victory in their Super League Super 8s clash at Langtree Park.
Doubles from Jack Owens, who also kicked for 10 points, and Atelea Vea proved crucial as Hull failed to follow up their Wembley triumph over Warrington Wolves with a win.
Despite taking an early lead through Mahe Fonua's genius try, nipping in on the blindside inside four minutes, a second-half surge saw Saints put on an additional 21 points to Hull's four.
Hull could now surrender their place at the top of the table if Warrington overcome Catalans Dragons in Perpignan on Saturday, and such a result would all but secure Saints a semi-final berth having opened up a six-point lead over the French side.
Denny Solomona took his try tally for the season to 35 with a hat-trick as Castleford Tigers defeated Wakefield Wildcats 46-22, though their top-four hopes were ended by the victory for St Helens.
All three of Solomona's tries came in the opening 22 minutes, while Luke Gale converted one of his own to take break the 1000-point mark in his Super League career.
Leeds Rhinos maintained their unbeaten record in the qualifiers with a 30-8 thumping of Salford Red Devils.
London Broncos were on the receiving end of a similar hammering as the lost 40-4 to Huddersfield Giants, who sit two points behind the Rhinos in second.