King's Lynn will take a ten-point lead into the second leg of their Knockout Cup Semi-Final against Sheffield after a brilliant 50-40 home win on Thursday.
At the 18th attempt, the PSH Environmental Stars finally got the better of the South Yorkshire side in any top-flight competition with a strong team showing.
Six of their seven riders were able to record at least one paid win each as they won 11 of the 15 heats against the reigning league champions.
Team manager Rob Lyon said: “It was a great team performance all the way through.
“With all due respect, I don’t think anybody expected us to beat Sheffield by ten.
“I appreciate that Sheffield have been a difficult team to beat these last few years but that will make a massive difference psychologically moving forward.
“They had their full team out but the boys took it to them to give ourselves a great chance.
“We’ve got a few meetings before then though and hopefully we can go on a bit of a run now.”
A 5-1 from Patryk Wojdylo and guest Richard Lawson over current world No.2 Jack Holder got the Stars off to a dream start before Simon Lambert and Anders Rowe turned a 5-1 to the visitors into a 4-2 in the hosts’ favour.
Nicolai Klindt and Rowe then delivered another 4-2 in Heat Four to open up an eight-point lead.
The visitors had reduced the gap to just two points after seven races.
Still, successive maximums from Niels-Kristian Iversen and Benjamin Basso over triple World Champion Tai Woffinden and then from Wojdylo and Lawson over 2012 World Champ Chris Holder saw them extend their advantage to ten.
The final five heats were all 3-3s with the Stars taking the chequered flag in four of those to help maintain that double-figure lead ahead of the decider at Owlerton Stadium on Thursday, June 27.
The PSH Environmental Stars travel to Leicester in the ROWE Motor Oil Premiership next Thursday (June 13, 7.30pm) with the next action at the Adrian Flux Arena on Monday, June 17 against Oxford.
King's Lynn 50: Nicolai Klindt 13, Patryk Wojdylo 11, Benjamin Basso 8+1, Niels-Kristian Iversen 7, Richard Lawson 6+4, Simon Lambert 3, Anders Rowe 2.
Sheffield 40: Jack Holder 10+1, Chris Holder 9+1, Tai Woffinden 6, Kyle Howarth 5+1, Josh Pickering 5, Jason Edwards 3+1, Dan Gilkes 2+2.