Whitlock recorded a one-hundred-percent finishing success rate in a 7-5 victory over the Scotsman, who had earlier drawn with compatriot Peter Wright.
Michael van Gerwen surrendered a 6-3 lead against Adrian Lewis in one of three draws at the Westpoint Arena.
Raymond van Barneveld and Dave Chisnall also drew, while Gary Anderson defeated Phil Taylor.
Simon Whitlock 7-5 Robert Thornton – Match Report
Michael van Gerwen 6-6 Adrian Lewis – Match Report
Robert Thornton 6-6 Peter Wright – Match Report
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