Two tries in the last two minutes gave Exeter a remarkable win at Worcester.
In a topsy-turvy first half, Luke Arscott went over for the visitors before tries from Craig Gillies and Miles Benjamin put Warriors ahead.
However, Bryan Rennie went over for the Chiefs on the stroke of half-time to restore their lead.
The boot of Andy Goode seemed to have won the game for the Warriors before Phil Dollman and Sireli Naqelevuki went over late on.
The win was all the more astonishing as Exeter also overcame the loss of two players to the sin-bin in the second half with wing Gonzalo Camacho fortunate to escape with a yellow card for a dangerous tip tackle.
Exeter scored the first try after 16 minutes when a clever crossfield kick from Ignacio Mieres was collected by Arscott to score.
Back came Worcester when Gillies was driven over from a line-out close to the Chiefs' line.
They scored a fortunate second when Benjamin overhit his kick which was clearly destined for the dead ball area but it cannoned off the crossbar and deflected to allow Benjamin to touch down.
Undaunted, Exeter hit back when Rennie waltzed past some poor defence for a splendid individual try.
Chiefs were dealt a double blow when firstly Camacho was yellow carded followed by Arscott for a deliberate offside.
But the Warriors failed to take full advantage and were made to pay by those two late tries.
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Warriors coach Richard Hill told BBC Hereford & Worcester:
"That's got to be a bad moment of the season.
"To have done the hard work and to be ahead with just a couple of minutes to go against a team on form, and then to lose our own scrum, is a massive blow.
"Exeter never gave up and played very well, and deservedly scored the try in the end."
Exeter Chiefs head coach Rob Baxter told BBC Radio Devon:
"There are a few rumours going around there was a knock on somewhere for our final try. But we said to the boys 'Let's go for a win'.
"And, if there's one guy that's going to make something happen five metres from the opposition line it's Sereli Naqelevuki, and the big man did us proud again.
"We fought and fought and fought, scored four tries, drove into fourth place in the Premiership, guaranteed Heineken Cup rugby next season. Credit to our group of players."
Worcester: Pennell; Garvey, Grove, Rasmussen, Benjamin; Goode, Perry (capt); Mullan, Lutui, Taumoepeau, Percival, Gillies, Best, Kvesic, Cowan
Replacements: Shervington, Porter, Douglas, Gulliver, Horstmann, Arr, Gray, Fatiaki
Exeter: Arscott; Camacho, Rennie, Dollman, Jess; Mieres, Thomas; Moon, Whitehead, Tui; Hayes (capt), Hanks; Johnson, Scaysbrook, Baxter.
Replacements: Clark, Sturgess, Budgen, Muldowney, White, Barrett, Steenson, Naqelevuki.