North Wales Crusaders suffered their first league defeat of the season after going down 18-10 at Hemel Stags.
The Welsh side still have a three-point lead at the top of Kingstone Press Championship One.
Crusaders were drawing 10-10 at half-time thanks to tries from Dan Birkett and Gary Middlehurst, plus Tommy Johnson's goal.
But Hemel tightened their grip in the second half to see off the visitors.
South Wales Scorpions slumped to a 32-36 loss at home to Oldham Roughyeds, with a Mark Hobson try on the final hooter clinching a thrilling win for the visitors.
Despite a brace from Connor Farrer, plus further tries from Joe Burke, James Greenwood, James Tutuila and Shae Lyon-Fraser, Scorpions were not quite able to make up a 26-16 half-time deficit.