The world number one and three-times world champion will face Jamie Jones in the last 32 after the Welsh world number 39 completed a 5-2 victory over Zhou Yuelong.
Former UK champion Judd Trump was more convincing in his first-round victory, emerging with a 5-1 win over world number 67 Martin O'Donnell courtesy of breaks of 54, 84, 54 and 73.
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O'Donnell contributed 54 and 55, but was powerless to prevent world number five Trump from securing a meeting with Gary Wilson in the last 32.
Slessor, who reached the Northern Ireland Open semi-finals before losing to world champion Mark Williams last November, certainly proved a tough assignment for Selby, who saw the Gateshead player level at 3-3 from 3-1 behind.
Selby - who lost the final of this event to Shaun Murphy in Haikou four years ago - claimed two frames on the black for a 3-1 lead with Slessor winning the third frame courtesy of a break of 62 boosted by a late fluke on the blue.
It was the first time Slessor has won a frame against Selby having suffered a 4-0 defeat at the Paul Hunter Classic and a 5-0 loss at the China Open over the past few years.
Slessor - ranked a rising 44 on the one-year ranking list - pinched the fifth frame before a run of 105 saw him restore parity at 3-3.
Selby then produced a 62 in the seventh frame, his highest break of the match, and timely enough to move one up with only a possible two to play.
Despite recovering three snookers in the penultimate frame, the doughty Slessor missed a brown needing the four remaining colours as Selby finally dragged himself over the line to reach the last 32 when a re-spotted black looked likely.
Not at his best, but certainly effective enough in the end.

Yushan World Open Round One results

  • Mark Selby 5-3 Elliot Slessor
  • Mei Xiwen 5-2 Simon Lichtenberg
  • Neil Robertson 5-1 Andy Lee
  • Judd Trump 5-1 Martin O'Donnell
  • Andrew Higginson 5-4 James Cahill
  • Anthony Hamilton 5-2 Mark Joyce
  • Mark Williams 5-1 Alexander Ursenbacher
  • Harvey Chandler 5-4 Kurt Maflin
  • Yan Bingtao 5-0 Stuart Carrington
  • Kyren Wilson 5-1 Paul Davison
  • Mark Allen 5-1 Lu Haotian
  • Ben Woollaston 5-1 Chang Bingyu
  • Xiao Guodong 5-1 Michael Georgiou
  • Joe Perry 5-4 Mike Dunn
  • Ding Junhui 5-3 Yuan Sijun
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