Leicester scored an 84th-minute try with 14 men to win at Bristol and make it 10 wins from 10 Premiership matches.
The Tigers were staring at defeat until they patiently worked the ball wide for Guy Porter to score in dramatic style.
Fitz Harding finished a Bristol counter but Nemani Nadolo scored after fine footwork to leave Tigers three behind.
Ioan Lloyd's try put Bristol 23-13 up but Julian Montoya went over from a rolling maul and George Ford marshalled play for Porter to give Tigers victory.
At 26-23 down a drop-goal would have been enough for Leicester to preserve their unbeaten record ...