Darryl Fitton stunned top seed Stephen Bunting by recording a 4-2 victory to progress to the BDO World Championship quarter-finals.
Fitton, 50, a two-time semi-finalist at Lakeside, took the first set 3-2.
But a strong second set showing - highlighted by a 167 checkout in the second leg - brought Bunting level.
Bunting looked to have taken control of the game as he won the third set, but Fitton fought back, winning the next three sets to reach the last eight.
Fitton will face eighth seed Wesley Harms in the next round after the Dutchman edged past Alan Norris 4-3.
Harms was pushed all the way by Norris, who had initially raced into a two-set lead before the former eventually found his form.
England's Robbie Green is also into the quarter-finals after the fifth seed eased to a 4-1 win over Scott Mitchell.
Green, who defeated 2012 champion Christian Kist in the first round, raced into a three set lead before Mitchell got off the mark.
Mitchell briefly threatened in fifth set as he went 2-1 up, but Green sealed his passage by claiming the set 3-2.
Green's opponent will be Tony O'Shea, who also comfortably progressed at the expense of Steve Douglas.
Douglas, playing less than a month after suffering a heart attack, lost 4-1 as O'Shea kept himself on target for a maiden Lakeside title.