Graeme Dott became made a 146 break as the resurgent Scot took charge of his semi-final against Mark Selby, while Neil Robertson is only two from victory against Ali Carter.
The 32-year-old from Larkhall, just outside Glasgow, had entered his clash with Masters champion Selby as the underdog, with his opponent tagged as the tournament favourite.
But after winning Thursday's opening session 5-3, Dott maintained his dominance to open up a 10-6 lead, and requires just seven more frames 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.
The 2004 runner-up secured a first Crucible crown in 2006, beating Peter Ebdon, and on the evidence of the first two sessions against Selby he is playing well enough to win again.
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 Northern Ireland'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.
Australian Neil Robertson started and finished with century breaks in the afternoon - a total clearance of 140 and 104 - and he stretched further ahead after the evening session against Essex's Ali Carter in their semi-final.
From 8-2 behind early in the day, Carter reeled off four frames in a row, however Robertson took the final two of the afternoon to reassert himself as the dominant force.
They resumed in the evening at 10-6 and Robertson took a tense final frame to pull further ahead to go 15-9 up - needing only two frames for victory.
