Woollaston, ranked 34th in the world, lost 4-2 to Thai Dechawat Poomjaeng, ranked 74th, in the afternoon session at the World Snooker Academy in Sheffield.
Forty-fourth-ranked Dave Harold went down 4-2 to Indian Aditya Mehta, while Jack Lisowski was another afternoon loser - 4-1 against Ian Burns.
In the morning Jamie Jones, the world number 39, went down 4-1 to Passakorn Suwannawat of Thailand, while Paul Davison secured a 4-2 win over 41st-ranked Michael White.
In the evening session veteran players Rory McLeod and James Wattana were among the players to bow out of contention.
The Welsh Open runs from 11-17 February in Newport, with a total prize fund of £250,000.
Jamie Jones 1-4 Passakorn Suwannawat
Barry Pinches 4-1 Simon Bedford
Gerard Greene 4-3 David Grace
Luca Brecel 1-4 Sam Baird
Michael White 2-4 Paul Davison
Liu Chuang 4-2 Chen Zhe
Ben Woollaston 2-4 Dechawat Poomjaeng
Dave Harold 2-4 Aditya Mehta
Yu Delu 0-4 Craig Steadman
Matthew Selt 4-1 Jordan Brown
Jack Lisowski 1-4 Ian Burns
Andy Hicks 3-4 Duane Jones
Cao Yupeng 2-4 Martin O'Donnell
Xiao Guodong 3-4 Justin Astley
David Gilbert 4-0 Thanawat Tirapongpaiboon
Rory McLeod 2-4 Gareth Allen
Mike Dunn 4-1 Liam Highfield
James Wattana 3-4 Daniel Wells
Adam Duffy 4-2 Mohamed Khairy
Anthony McGill 1-4 Michael Wasley