Exeter snatched a second successive home win with the last play of the game to thwart Harlequins' stunning second-half comeback.
Two weeks ago it was Patrick Schickerling who popped up with a late, late try to beat champions Leicester, and this time it was Wales international Christ Tshiunza as the Chiefs claimed a 43-42 victory.
The referee had to check a possible forward pass in the build-up by Stuart Hogg before awarding the try, much to the dismay of Quins, who had come storming back from a 24-point half-time deficit to lead in an amazing repeat of the 2021 Premiership final.
Exeter picked up from where they had left off in their previous home game against Leicester, and were in devastating mood in the opening quarter. Former England prop Harry Williams got the first try after only four minutes, driving over from close range.
Seven minutes later, more good play from backs and forwards created the opportunity for scrum-half Stuart Townsend to snipe over, and in the 22nd minute Tshiunza outpaced two defenders down the left touchline and cut inside full-back Tyrone Green to run in behind the posts. Joe Simmonds converted all four - to add to a seventh-minute penalty - and Chiefs led 24-0.
The only real sniff Quins had of a try came from the restart kick following Simmonds' penalty, when Luke Northmore gathered the ball, raced towards the corner and got it down, but a superb tackle by England full-back Jack Nowell just forced the centre into touch.
The one area of concern for Exeter was their scrum, where Harlequins were collecting plenty of penalties, and the visitors eventually got a foothold in the game with a try in the left-hand corner by Cadan Murley, improved by England fly-half Marcus Smith.
Quins continued to look dangerous in the lead-up to the break but had the stuffing knocked out of them two minutes from half-time when young centre Lennox Anyanwu dropped the ball in midfield and Exeter fly-half Harvey Skinner picked it up and ran 40 metres to score in the corner for the bonus-point try.
Simmonds kicked another superb conversion to maintain his 100 per cent record with the boot, and Exeter led 31-7 at the interval. After the Chiefs had spent the opening few minutes of the second period camped in Quins' 22, the expected second-half onslaught began from the comeback kings of English rugby.
They scored two tries in two minutes - Murley setting up Green for the first before Green returned the favour for Murley - and with Smith converting both, the gap was down to 10 points.
That became three points when Northmore showed great pace to race in from 50 metres, converted by Smith, and then he added another far too easily as he sliced through the Exeter defence after the game had gone to uncontested scrums following injuries to both of Quins' hookers, and with Smith converting for a 35-31 lead, Sandy Park was stunned.
England prop Schickerling got the Chiefs back in front with a try, but Quins responded with a cross-field kick from Smith putting in Joe Marchant for a try to restore the Londoners' advantage, only for Tshiunza to strike again at the death.
