The 'Jester from Leicester' won the first session of his match against Xiao Guodong 6-2 and shared the evening's eight frames to maintain the advantage in the best-of-25 contest.
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However, it could have been worse for his Chinese opponent, who won the last two frames on Sunday evening to trail 10-6.
Elsewhere, there was little to choose between world number eight Marco Fu and number nine Neil Robertson - with the winner of this contest facing either Selby or Xiao.
Fu hit back from 4-1 down to head into the evening session against the Australian locked at 4-4, with a 118 the start of his recovery - and the first two frames of the evening were shared.
The Hong Kong player then took the lead for the first time in the contest when a break of 72 helped him to win the 13th - but the see-saw nature of the contest was to continue.
Robertson won the next two to regain the lead, only for Fu to land the 16th and ensure the pair were level again, at 8-8.
Earlier, Stephen Maguire ended Rory McLeod's hopes of further progress with a session to spare.
Maguire beat McLeod, the first round conqueror of pre-tournament favourite Judd Trump, 13-3 to reach his fifth Crucible quarter-final - but his first since 2012.
A break of 119 in the ninth frame was the highlight for Maguire, who will face Barry Hawkins or Graeme Dott for a place in the last four.
Hawkins, on his 38th birthday, was in impressive form early in the evening, turning a 5-3 advantage into a 9-3 lead against the 2006 champion.
Scot Dott then won three successive frames to reduce the deficit to 9-6 and keep alive his hopes of progressing - with a 105 clearance in the 15th the highlight.
However, Hawkins took a nervy final frame to lead by four.
Sunday's Crucible scores
Mark Selby (1) 10-6 Xiao Guodong
Frame scores: 75-19 (67), 88-29 (58), 25-93, 80-5, 70-17 (51), 80-40 (76), 8-89 (89), 72-49, 0-89 (89), 62-28 (62), 0-131 (131), 68-54 (Selby 68, Guodong 54), 70-39 (57), 71-35, 51-67 (Selby 51), 16-62
Neil Robertson (9) 8-8 Marco Fu (8)
Frame scores: 105-1 (105), 6-66, 86-0 (62), 78-31 (62), 90-30 (90), 1-119 (118), 14-98 (60), 47-59, 68-46, 8-121 (109), 92-6 (91), 33-94 (64), 0-73 (72), 92-0, 70-4 (58), 2-102 (56)
Graeme Dott 6-10 Barry Hawkins (7)
Frame scores: 73-16, 60-69, 51-63 (Dott 51, Hawkins 50), 13-81, 79-43 (64), 8-72 (54), 0-92 (91), 6-91, 69-24, 57-70 (Dott 57, Hawkins 70), 28-59, 66-1 (65), 59-41 (59), 109-8 (105), 50-62
Stephen Maguire 13-3 Rory McLeod
Frame scores: 72-43, 94-31 (67), 56-14, 72-43, 85-6 (71), 0-73 (73), 45-63, 72-23 (63), 118-21 (114), 87-48, 43-89, 68-20 (61), 106-16 (90), 71-60 (McLeod 60), 87-28 (57), 66-52
