Riley B stunned second-placed HCC A with a stunning 3-0 victory in Division 2.
Riley, who were rooted to the bottom with just two wins all season produced a terrific display to seriously dent HCC’s title ambitions.
The losers are now five points off the top.
Newcomer Bob Lacey (+100) beat Pete Brooks (+110) 100-64 to give Riley an early lead.
Doug Baker (+60) then crushed Dough Howse (+30) 200-124, before Bob Hayward (+70) ran away from John Williams (+70) 150-69 to complete the whitewash.
They do, however, remain bottom, but are now just four points off second.
Leaders Ashton stay top after a 2-1 win over Oracle.
Craig Pullen (+110) won his first match for Oracle when he inched past Keith Maskens (+50) 150-144.
But Ashton won the next two games when John Street (+60) beat Ted Milsom (+50) 150-115, and then Pete Fenn (+50) saw off Gordon Cook (+70) 150-128.
In Division 1, Riley A continue to lead the way after a 2-1 win over CCC A.
Matthew Challen (+30) held off Dick Hashman (scratch) 200-166, but Terry Cook (+20) levelled when beating Allan Copelin 200-150.
In the deciding game, Malcolm Bough (+50) came from behind to clinch the match against Keith Pearce (+50) 150-139.
Fieldside crushed Eynsham 3-0, with Norman Woodcock, Mike Chapman and Bob Chivers all winning.
New Club beat Thame 2-1, despite losing the opening game when Nigel Bossom (scratch) came from way behind to overtake Dave White (+80) and win 200-174.
Alan Mander and Alan King secured victory.
Results Riley 2, CCC A 1; Oracle 1, Ashton 2; New Club 2, Thame 1; Fieldside 3, Eynsham 0; HCC A 0, Riley B 3.
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