Paris - Three-time winners Leinster were left battling for survival in this season's European Champions Cup when they slumped to a 19-16 defeat at Bath on Saturday, their second successive loss.
The defeat, which followed last week's 33-6 mauling at the hands of Wasps in their Pool 5 opener, left the Irishmen facing back-to-back games with defending three-time champions Toulon to keep their hopes alive.
"It's going to be tough. We just need to park Europe for the next couple of weeks, and try to get a bit more confidence in the Celtic League," said Leinster coach Leo Cullen.
Flyhalf star George Ford kicked the match-winning penalty for Bath from 40 metres with three minutes left at the Recreation Ground.
It was his fourth successive kick of the game and came just moments after Johnny Sexton had missed a difficult 55-metre penalty for Leinster which fell just short with the match level at 16-16.
Bath, whose opening game in the tournament in Toulon was called off last week in the aftermath of the Paris terror attacks, and their Irish visitors were level at 9-9 deep into the second half.
But Bath edged ahead on the hour through a penalty try awarded by French referee Jerome Garces as Leinster's scrum continued to buckle.
Ford popped over the extras before replacement Josh Van Der Flier went over for Leinster just two minutes after coming onto the pitch.
Ford had the last word with his 14-point haul to condemn Leinster to their first back-to-back opening losses in Europe in two decades.
The victory was also sweet revenge for Bath after they had lost 18-15 to the powerful Irish side in last season's quarter-finals.
"We showed our inexperience at 16-9 up," said Bath coach Mike Ford, the father of George.
"We were in control of the game, but we stupidly did things that let them back in.
"I am pleased we won against a Leinster side full of internationals. Our scrum was awesome -- Henry Thomas and Nick Auterac were outstanding -- but we can't afford to give teams easy outs and chances to score points like we did today."
Four-time champions Toulouse lost their opener 32-7 at Saracens last weekend but hit back on Saturday with a 24-18 win over fellow French side Oyonnax.
All of the game's five tries came after the interval with Timoci Matanavou, Maxime Medard and Gael Fickou scoring for Toulouse.
Two-time champions Leicester defeated Stade Francais 33-20 last week and followed it up on Saturday with a 36-3 win at Pool 4 whipping boys Treviso with Tongan winger Telusa Veaninu grabbing a brace.
It was the Tigers' second successive bonus-point win.
Racing 92, who will welcome World Cup winner Dan Carter into their ranks next month, started their Pool 3 campaign with a 29-12 win at the Scarlets in Wales.
Racing's scheduled opener at home to Glasgow last week was cancelled after the Paris attacks but they were quickly into their stride on Saturday, sprinting to a 26-0 lead at the break.
They scored four tries in a dominant first half through Maxime Machenaud, Joe Rokocoko, Chris Masoe and Marc Andreu.
Racing played most of the second half with 14 players after France flanker Bernard le Roux was red-carded for stamping on Phil John.
Aled Thomas and Lewis Rawlins scored two tries for the Scarlets but the Welsh side couldn't close the gap even when Racing were temporarily reduced to 13 men when Ben Tameifuna was sin-binned.
Northampton, the 2000 champions, lead the way in the group after a 26-15 win in Glasgow followed on from their 15-11 victory against Scarlets in their first game.
Samoan star Ahsee Tuala scored two tries for the Saints.
On Friday, Saracens fought back from 9-0 down to defeat Ulster 27-9 at a rainswept Belfast to make it two wins from two in Pool 1.
Champions Toulon will make their bow in the competition away to Wasps on Sunday.