Valley Cougars tasted defeat for the first time in nine matches as they went down 28-22 in the RFL Conference South at Nottingham Outlaws on Saturday June 27.
The Welsh side, based in Treharris, still remain top of the league, but Nottingham are now just two points behind them with a game in hand.
Nottingham did well to come back from 16-10 down as Cougars took advantage of the home side having a man in the sin-bin just before the break.
However, complacency set in for the Welsh side after the break as they took their foot off the gas and the Outlaws took advantage to secure a dramatic win.
George Matthews led the way for Nottingham with a brace of tries with Adrian Chaima, Oliver Crick and Adam Cunliffe, who also kicked four goals, also crossing.
The Cougars replied with two tries from Craig Lewis and one each from Ethan Coombes and Yousif Suliman. Danyl Davies converted three times.
Cougars coach, Dafydd Hellard, said: “In hindsight the defeat will be good for us. We’ve become a bit complacent. Now we can regroup and prepare for another big away game against Sheffield Hallam Eagles next week.”