Gareth Thomas of Toulouse is tackled by Mike Catt
Toulouse: (20) 37
Tries: Jauzion, Garbajosa, Fritz, Montauriol
Cons: Elissalde (3), Courrent
Pens: Elissalde (3)
London Irish: (10) 17
Tries: Armitage, Roche
Cons: Everitt, Armitage
Injury-hit London Irish gave Toulouse a run for their money in France before eventually being overpowered in their Heineken Cup Pool Five clash.
The Premiership side fought hard in the final 10 minutes to try to claim a losing bonus point but to no avail.
Fly-half Riki Flutey missed the match, while Barry Everitt and Mike Catt were also injured during the game.
The Exiles' second straight loss means their quarter-final chances are now hanging by a thread.
Even wins in all four remaining games against Ulster (twice), Llanelli and Toulouse will probably not be enough.
Toulouse led 27-10 early in the second period following tries from Yannick Jauzion, Xavier Garbajosa and Florin Fritz.
But it was not until injury time that a bonus point score arrived when substitute forward Jean-Francois Montauriol ploughed over.
Scrum-half Jean-Baptiste Elissalde chipped in with 15 points from the boot and substitute Valentin Courrent kicked the final conversion, yet the final margin was harsh on the Exiles.
Ultimately, they had to settle for tries by full-back Delon Armitage and lock Kieran Roche.
Armitage slotted a conversion after he took over kicking duties from Everitt, who earlier landed a penalty and conversion.
The Exiles were dealt a blow when Flutey was forced to withdraw after suffering a groin strain during kicking practice on Saturday.
Everitt, his replacement, was hit by a leg problem and missed the second half, while Catt suffered a recurrence of a calf injury.
London Irish director of rugby Brian Smith: "I thought it was a courageous effort, but Toulouse showed their real class and pushed us to the limit.
"We knew that we needed a defensive improvement and we got it, but it is now a tough ask for us to get to the quarter-finals.
"Mike Catt's injury is a recurring calf muscle injury. It happened at Newcastle last month, and then again when we went to Sale.
"Having lost Barry Everitt as well, it meant we had to play with two scrum-halves, but I thought they made a good fist of it."
Toulouse: Garbajosa; Clerc, Fritz, Thomas, Heymans; Jauzion, Elissalde; Human, Lacombe, Perugini; Albacete, Millochlusky; Dusatoir, F Maka, Pelous.
Replacements: Courrent for Elissalde (79),
Hasan for Human (33), Bru for Lacombe (57), Baby for Albacete (76), Montauriol for F. Maka (57), Lamboley for Pelous (62).
Not Used: Bouihlou.
Sin Bin: Heymans (71).
London Irish: D Armitage; Ojo, Mapusua, Catt, Tagicakibau; Everitt, Hodgson; Hatley, Paice, Lea'aetoa; Roche, J Hudson; McCullen, Danaher, P Murphy.
Replacements: Rees for Catt (43), Pedro Tiesi for Everitt (41), Magne for Danaher (41), Leguizamon for P Murphy (67).
Not Used: Skuse, Russell, Johnson.
Referee: Nigel Owens (WRFU).