Warrington Wolves had displaced Hull at the summit by hammering Leeds Rhinos 52-18 on Friday and will have had hopes of maintaining that position when St Helens led 18-14 at half-time at the KC Stadium.
Hull FC return to Super League summit
Hull FC moved back to the top of Super League as an impressive second-half showing sealed a 32-24 win over St Helens on Saturday.
But, on a day in which Hull City returned to the Premier League, the hosts provided more for the locals to celebrate, outscoring St Helens three tries to one after the restart to turn things around.
Hull added to tries from Gareth Ellis and Mahe Fonua and a Marc Sneyd penalty in the first half as Carlos Tuimavave, Scott Taylor and Danny Washbrook all went over in the second 40 to restore their two-point advantage at the top.
However, it was a disappointing day for city rivals Hull KR, who suffered a third defeat in four matches at the hands of high-flying Catalans Dragons, losing 34-16 in the south of France.
The Dragons did most of the damage in the opening period in Perpignan, crossing five times in the first 40 to open up a 28-6 lead.
Jodie Broughton, Todd Carney, Lucas Albert, Louis Anderson and Tony Gigot scored four-pointers to effectively end the game as a contest before half-time.
Gigot then added a second 10 minutes from time as Catalans stayed within two points of the leaders in third.
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