Whitlock is yet to drop a set in the tournament after seeing off Kevin Painter in the afternoon session, while Webster enjoyed a brilliant triumph over Raymond van Barneveld.
Simon Whitlock 4 – 0 Kevin Painter – Match report
Mark Webster 4 – 3 Raymond van Barneveld – Match Report
Robert Thornton missed out on a place in the last eight, suffering defeat at the hands of Wes Newton.
Whitlock will return to action on Saturday evening, when he faces Ian White for a place in the last four.
Webster faces either Michael van Gerwen or Gary Anderson on Sunday.
By Chris Murphy
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