Harlequins upset the odds with a surprise Heineken Cup success over the four-time European champions.
Two tries from Mike Brown, either side of Joe Gray's first-half effort, plus 16 points from the boot of Nick Evans, sealed a famous 31-24 win that blew Pool Six wide open.
Scrum-half Jean-Marc Doussain scored a try among his 15 points as Toulouse claimed a losing bonus point that kept them top of the group, a point ahead of Harlequins, while Gloucester are also now back in contention to qualify for the quarter-finals.
O'Shea said: "Right now this feels like we've won a cup final but it's a pool game and we have to make sure we keep learning.
"The resolve the players showed was incredible. We have a good record away from home but we knew coming here we were going to have to ride our luck at times in the face of wave after wave of pressure.
"They missed a couple of kicks but we had the ambition to play and everyone involved with Harlequins must be very proud of the effort of the players.
"We won't stick our heads in the sand and say it was a perfect performance but these are the days that make the Heineken Cup and the games you are judged on."
Harlequins had gained a surprise 15-3 lead after just 18 minutes when Brown and Gray both crossed as a result of well-placed kicks by fly-half Evans.
Evans' opposite number Luke McAlister, however, scuffed three chances at goal before Toulouse hit back just before half-time through Yoann Maestri.
Jean-Marc Doussain took over the kicking duties and handed Toulouse a 19-15 lead with a strong of penalties as Harlequins were forced to dig deep not to concede a second try.
However Tom Williams turned over possession with a telling tackle on Vincent Clerc, from which Brown scored Harlequins' third - and decisive - try in the 62nd minute.
O'Shea said: "We have shown how quickly we can learn at this level. We were disappointed with a few things from the previous game at the Stoop but we got our line-speed in defence right and that pressured them [Toulouse] into mistakes.
"When you look at their bench, they were bringing on more power after power but when you're in the match, you get carried away with adrenaline and that's what happened here.
"We got a few breaks and then Tom Williams came off the bench and produced a game-changing moment that got us right back into the game when we needed it most. Then we held out for a big result."
Harlequins captain Chris Robshaw revealed a change of mindset sparked the performance which delivered a stunning win.
Robshaw told BBC Sport: "Last week we were in too much awe of them [Toulouse] but today we gave it everything.
"We stuck in there especially in the second half when they seemed to be gaining the momentum."
Toulouse scrum-half Jean-Marc Doussain said: "We can't lose our heads, we have our destiny in our own hands.
"It's a pity we couldn't win, having won there last week. If we had taken our chances we would have won.
"We knew how Harlequins would play, but perhaps they raised their level compared to last weekend.''
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