Smith saw off Nathan Rafferty in a close affair which saw the St Helens ace average just over 100 as he brought the young Northern Irishman's run to an end.
Durrant had a similarly tough task in seeing off Corey Cadby with the match going to a final deciding leg which 'Duzza' just edged out with a 102 average.
De Zwaan averaged over 100 as well with 103 in a 6-3 win over Steve Beaton in an impressive win for 'The Black Cobra'.
In fact, six out of the eight winners in the last 16 posted ton-plus averages while Gerwyn Price lost with a 105.2 average showing the ridiculous standard on the Players Championship series this year.
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