Luke McAlister kicked 18 points to give the hosts victory in a real arm-wrestle between two sides who between them boast 11 final appearances and six titles in Europe's premier club competition.
The Tigers had looked set to reach the halfway stage with a lead thanks to a trio of penalties from Toby Flood, only to shoot themselves in the foot in the 38th minute.
Gael Fickou provided a moment of sheer quality in what was otherwise a battle between the two sets of forwards, seizing on a Thomas Waldrom knock-on to grab the only try just before the interval.
The teenage centre scooped up the loose ball and then comfortably out-paced Anthony Allen to his own kick, meaning Toulouse went in at the break 11-9 ahead despite spending 10 minutes down to 14 men.
Guthro Steenkamp was rightly shown a yellow card by referee Nigel Owens after tripping Leicester full-back Scott Hamilton as he attempted a quick re-start.
Yet McAlister contributed two first-half penalties before Fickou's try and then booted over a further 12 points after the break, as Toulouse's powerful pack turned the screw on their opponents.
Indeed, only some desperate defending from Leicester substitute Matt Smith, who somehow dived on the ball over the try-line to deny Yohan Huget what seemed a certain try, prevented the final margin being even greater.
Richard Cockerill's side will return home to lick their wounds before welcoming Ospreys, winners over Bennetton Treviso on Friday night, to Welford Road - they'll know they can ill-afford a slip up on home soil if they are to reach the knockout stages.
What will worry Cockerill is that his Tigers looked rather toothless in attack, their best opportunity for a try coming when Flood just failed to squeeze in at the right corner following a shocking clearance from Clement Poitrenaud.
They failed to muster a single point in the second half, though that could have been different had Ben Youngs not opted to take a quick tap when 14-9 down.
It was a rare opportunity in an otherwise difficult 40 minutes for the Aviva Premiership side as the conditions became tougher. Instead it was Toulouse who were left singing in the rain at the final whistle.
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