Four-time champion Mark Selby is being made to work for his last-16 place at the World Championship - he leads Matthew Selt 9-8.
The winner of that one will play Robert Milkins in round-2 after he came from 7-2 down to beat Joe Perry 10-9.
Mark Williams ended the first session of his second round match level at 4-frames apiece with Luca Brecel.
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This evening sees Mark Allen begin his second round tie with 2015 champion Stuart Bingham.