London Broncos' brave bid to retain their Super League status came up short, while Salford Red Devils claimed third place in the table.
Jay Pitts' late try means London Broncos remain in with a chance of beating the drop, while also leaving Hull KR in deep trouble.
A 36-10 win over London Broncos means Leeds Rhinos can put a forgettable Super League campaign behind them and not worry about relegation.
Victory on the road at Catalans Dragons sees London Broncos join three other teams on 18 points at the foot of Super League.
Castleford Tigers climbed to fifth place in Super League as a four-try display saw off a London Broncos side who led in the early stages.
Salford Red Devils cruised against London Broncos, while Hull KR beat Castleford Tigers in dramatic circumstances.
St Helens have only lost three games all year in Super League, but two of those defeats have come at London Broncos.
Hull FC surged 34-0 ahead before holding on for a 35-22 victory over Super League's basement dwellers on Thursday.
A dominant first-half display from Warrington Wolves saw them blow struggling London Broncos away on the road on Saturday.
Leeds Rhinos won their first game without Kallum Watkins, defeating Catalans Dragons 31-12 at Headingley on Sunday.