Exeter's hopes of European glory were almost extinguished as they crashed to a surprise 27-19 defeat at the hands of Gloucester at Sandy Park.
The defeat left Exeter without a win in their first three European matches and leaves them rooted to the bottom of Pool 2 with only three points and with difficult away trips to Munster and Gloucester still to come.
Gloucester were deserved winners with tries from Willi Heinz, Jaco Visagie and Ben Morgan. Danny Cipriani kicked two penalties and two conversions with Billy Twelvetrees adding a conversion.
Exeter's tries came from Nic White, Tom Lawday and Don Armand, with Gareth Steenson adding two conversions.
Exeter took the lead in the seventh minute with a superb try after the visitors were turned over deep in the Chiefs' half.
Alex Cuthbert, Ben Moon, Santiago Cordero and Henry Slade all made crucial contributions to a 65-metre move, which culminated in Armand scoring.
Gloucester soon responded in style with an excellent try after Matt Kvesic's ill-judged kick ahead gave Ollie Thorley to chance to counterattack.
Thorley danced past two defenders before being hauled down by a brilliant cover tackle from Cuthbert but Heinz was up in support to score.
Cipriani converted to give his side a 7-5 lead at the end of an entertaining first quarter before Heinz split the defence, only for Henry Trinder to knock-on to spoil a promising position.
The second quarter was not as eventful as the first as the rain temporarily arrived to make conditions more difficult with both scrum-halves, Heinz and White, surrendering valuable territory by kicking straight into touch.
Owen Williams had a chance to extend Gloucester's advantage but his 60-metre penalty attempt went badly astray, before Cipriani resumed the kicking duties to knock over a simple penalty and give his side a five-point advantage at the interval.
That lead did not last long as, within a minute of the restart, Exeter had their second try. From the kick-off, Gloucester were turned over for White to spot a gap and run 20 metres to score.
Steenson converted before Cipriani put the visitors back in front with his second penalty but the momentum was now firmly with Exeter, whose pack took looked to be taking control.
They were able to replace two international props, Moon and Greg Holmes, with another two in Alec Hepburn and Tomas Francis, to keep Gloucester penned in their own half but the hosts could not capitalise.
Exeter also withdrew Slade and Kvesic but the loss of key line-outs cost them vital possession and Gloucester remained in front going into the final quarter.
After 62 minutes minutes, Gloucester scored a crucial second when another timely burst from Thorley set up the chance for Cipriani to send Visagie through a gap with a delightful pass, before the hooker crashed over the line for his first try for the club.
Cipriani was replaced by Twelvetrees as Gloucester attempted to shore up their defence, but there was no need as Morgan forced his way over from close range to seal a famous victory with Lawday's late try a mere consolation.