Four-time European club champions Toulouse failed to make the quarter-finals of this year's competition when they slipped to a 27-26 defeat to Montpellier in their final group match on Sunday.
Toulouse centre Gael Fickou (L) and centre Florian Fritz tackle Montpellier's New Zealand winger Rene Ranger (C) during the European Champions Cup match in Montpellier, southern France on January 25, 2015
Bath's 20-15 win over Glasgow saw them leapfrog Toulouse to finish top of Pool 4 and climb into the last eight.
Bath are joined by Northampton, Wasps and Saracens -- the first time since 1998 four English clubs have made the knockout stages of Europe's elite competition.
Montpellier's victory meant Pool 1 leaders Clermont qualified along with Saracens before they two teams even played later on Sunday. Clermont went on to win 18-6.
"After a worthy campaign with two away wins, it's strange and frustrating to find ourselves fall by the wayside," said Toulouse head coach Guy Noves.
"We didn't qualify because we let up at the end of the competition, notably last week where we really slipped up (35-18 loss to Bath)."
Toulouse, who are also struggling on the domestic front where they are only seventh in the Top 14 and currently out of the qualifying places for the play-offs, needed the win to go through.
And they had every chance to stamp their authority on a disappointing Montpellier side who had only racked up two points from their previous five games.
- Sailing -
Toulouse even led 20-9 and appeared to be sailing to victory after 43 minutes, with converted tries from Clement Poitrenaud and Toby Flood on the board.
But two tries for Montpellier by Lucas Dupont, in the space of the next seven minutes, one of them converted, put the home side ahead by a single point.
Flood kicked two more penalties, but Montpellier replied on each occasion, first through fly-half Benoit Paillaugue and then Ben Lucas, as Toulouse led 23-21 and then 26-24.
But with 12 minutes left on the clock, Lucas stole victory with a final penalty to complete his tally of 11 points for the afternoon.
Clermont meanwhile, ensured a home quarter-final by beating Saracens 18-6 at their Marcel-Michelin Stadium to keep their dream of a first European title on track.
The French side finished top of Pool 1 with 22 points, in a group that included three of the last four semi-finalists -- Clermont, Saracens and Munster -- and will play Northampton on April 4 or 5.
Saracens also qualify with 17 points, but will travel to French club Racing-Metro in the last eight.
The English side, who whipped Clermont 46-6 in the semi-finals last year, dominated the first half hour, before losing fly-half Owen Farrell to a knee injury.
Farrell had missed a penalty before his injury and his replacement Charlie Hodgson also struggled with his kicking.
Clermont took the lead when Farrell gave away a penalty in the seventh minute allowing Camille Lopez kick the French ahead.
English back Nick Abendanon touched down the first of Clermont's two tries after 31 minutes after picking the ball off scrum-half Morgan Para. Lopez converted to make it 10-3 at half-time.
- Big moment -
Hodgson reduced the deficit to four points with a penalty after the break.
But the French added their second try in the 53rd minute as substitute Vincent Debaty got through, although Lopez failed to convert.
Jamie George prevented Clermont from adding to their tally by charging down Brock James' late drop-goal attempt, but the Australian got a penalty kick in the 77th minute.
"It's a big moment for our group," said Clermont hooker Benjamin Kayser.
"We achieved an exploit at Munster, we had a complicated match at Sale, and there was psychological wear and tear.
"This evening, honestly, we didn't have a great match, but we put a lot of energy into it, and were so solid in defence that we didn't crack."
Wasps, runners-up in Pool 2, completed the line-up as one of the three best second-placed sides, after Saturday's 20-20 draw against three-time champions Leinster.
Leinster squeezed through as Pool 2 winners meaning Ireland avoided being without a team in the knockout stages for the first time in 17 years.
Munster, meanwhile, won their dead rubber against Sale 65-10 at Thomond Park.
Both sides were out of the running in Pool 1, but the Irish province nevertheless claimed a bonus-point victory that included eight second-half tries.
Quarter-final draw
Racing Metro (FRA) v Saracens (ENG)
Toulon (FRA) v Wasps (ENG)
Clermont (FRA) v Northampton (ENG)
Leinster (IRL) v Bath (ENG)