The 'Rocket', who is tied at 8-8 with Dott overnight, had been dogged with tip problems throughout the tournament before matters came to a head in the 14th frame of the best-of-33 showdown at the Crucible Theatre.
O'Sullivan went back to his chair when leading 22-21 and it looked as if he picked away at the tip until it came away from the cue.
Dott cleared up to win the frame with a superb 66 break but O'Sullivan immediately left the arena to carry out repairs with his mentor Ray Reardon. Snooker legend and now BBC pundit Steve Davis slammed the tactics employed by O'Sullivan, who had looked ill at ease all through the session.
The six-time world champion said: "It looked like Ronnie was picking at the tip to get it off.
"It is unfair on Graeme Dott who has just started to hit some rhythm. In other sports can you deliberately halt progress? Is there a precedent for saying 'You should lose a frame?'"
Another former world champion, John Parrott, echoed Davis' sentiments, saying: "Let's say the tip got help in coming off. I am not very happy with that. He should not be allowed to do that."
A 15-minute delay followed as O'Sullivan had a new tip installed.
Dott went to the practice room before play resumed and O'Sullivan looked a different player as he knocked in a 124 break in the next frame to move 8-7 ahead.
But O'Sullivan, who had been given snooker's equivalent of a yellow card for swearing in a previous match with Ryan Day, did not look happy with life and asked for a noisy spectator to be moved before the mid-session interval. The person was later allowed back into the auditorium.
In the last frame of the day Dott, Scotland's remaining hope in Sheffield, levelled the match with a break of 74.
In the other semi-final, Peter Ebdon produced the kind of stunning snooker which could carry him to a second world title as he took an impressive 15-9 lead against Marco Fu.
Ebdon demonstrated the fluent side of his game lacking in a turgid and slow-moving opening session to move into a 9-7 lead in the best-of-33 showdown.
The 2002 champion reeled off two centuries and five other 50-plus breaks but Fu, appearing in his first semi-final at Sheffield, showed his mettle in the final frame of the session with a superb 70 clearance to prevent himself from falling four behind after Ebdon had led 67-0.
The initial eight frames had been a grind, spanning nearly four hours and prompting one spectator to shout out 'it's like watching paint dry' which earned him a reprimand from referee John Oomen. But a new day seemed to bring a fresh approach, with Ebdon and Fu both showing more positive intent.
Fu, bidding to become the first Asian to reach the world final, broke down on 17 in the opening frame and Ebdon took advantage with a composed 68.
He went two frames clear in the match for the first time after taking advantage of a poor safety shot by 28-year-old Fu in the next.
Ebdon hit a break of 94 in the final frame before the interval and the match continued in a similar vein after the break with Ebdon's 74 clearance putting him 8-5 ahead, before Fu rallied to end the session 9-7 behind.
But then Ebdon moved up a gear again winning four frames on the trot, that included breaks of 122 and 93 to move 13-7 ahead. Fu pulled two frames back but Ebdon remained in control and finished the night 15-9 ahead.