Callum Sheedy's last-gasp conversion gave Bristol a stunning 35-33 comeback victory over Harlequins to extend their lead at the top of the English Premiership on Saturday. Two tries in the final minutes of the game snatched victory from their title rivals, who had looked almost certain to inflict just a second home defeat on Bristol this season. But the leaders showed their perseverance for a second successive week to boost their bid for a maiden Premiership crown. It was an all-action, back-and-forth encounter between the Premiership's first and third-placed teams, as Six Nations stars Sheedy, Kyle Sinckler, Ben Earl and Joe Marchant all returned to club duty. Bristol led 21-17 at the break after tries from Dave Attwood, Fitz Harding and Piers O'Conor. Quins replied with a penalty try and a Danny Care try. Care's drop goal, a Marchant try and a Marcus Smith penalty put the visitors 33-21 ahead with just eight minutes remaining. But a penalty try and Sinckler's last-minute score pulled Bristol level, with Wales international Sheedy holding his nerve to secure the win. Bristol are 12 points clear of second-placed Exeter, who lost 34-18 to Gloucester on Friday. Bristol director of rugby Pat Lam, whose side also produced a late fightback last week against Northampton, told BT Sport he had confidence in his team's character. "With 10 minutes to go, when they scored their try, the message went on, I said 'Boys, we've been here before'," he said. "They knew the message then when we know we've got to get back into it, it's just get the detail right, get jobs right, don't panic and they did it perfectly," he added. jw/jc