Dott maintained his dominance to open up a 10-6 lead, and requires just seven more frames today to secure a third appearance in the Crucible final.
Dott has been reborn as a snooker player since the darkest days of his depression, which followed several episodes of strife in his private life.
And by reaching the semi-finals in Sheffield he guaranteed himself not only a top-16 ranking but another shot at world title glory.
Dott’s masterful near-maximum effort came in the 13th frame, taking an early pink before following each other red with the black.
Until this World Championship the event had never seen a 146 – there have been nine 147s – but Antrim’s Mark Allen made one in his second-round match against Mark Davis to create history.
Unless there is a maximum, Allen and Dott will be sharing the £10,000 top break prize. By drifting to 48th in the provisional world rankings in late 2008, Dott was moving close to disappearing into snooker oblivion, but his motivation has returned and the form he has shown over the past fortnight has amazed every observer.
Far from the dour player he has been harshly portrayed as in the past, his game has been attack-minded.
Selby lost the opening frame to Dott this afternoon despite having a break of 54. But the Leicester potter fought back in the next with a run of 63, after an earlier 66 from Dott looked to have made him favourite.
Selby closed the gap to 6-5, however Dott then took over the heavy scoring, making an 84 break to restore his two-frame advantage before gunning in the 146.
The next frame was less memorable, Selby taking a low-scoring one but Dott battled back from 52 behind to win the penultimate of the session with a break of 66, and then capped his afternoon with 86 to develop his healthy lead.
Earlier, Australian Neil Robertson started and finished with century breaks a total clearance of 140 and 104 – as he retained a four-frame advantage over Essex’s Ali Carter in the other semi-final.
From 8-2 behind early in the session, Carter reeled off four frames in a row, however Robertson took the final two to reassert himself as the dominant force.