The Tigers won the battle of the East Midlands to claim the first silverware of the English club rugby season and a place in the Heineken Cup.
The match was settled soon after half-time as wing Scott Hamilton ran 80 metres after intercepting an ambitious pass from Saints fly-half Stephen Myler.
Teenage fly-half George Ford, who kicked a match tally of 16 points, had kept the Tigers in touch with three penalties before flanker Steve Mafi gave them the lead for the first time in the 26th minute.
Northampton, winners of the competition two years ago, did not manage a try until five minutes from time, through lock Christian Day.
Sunny Sixways provided a perfect stage but with a chilly north-westerly wind aiding Northampton from the kick-off. After a 'sighter' from a difficult angle, Myler opened the scoring at the second attempt from near halfway in the sixth minute.
Although Leicester mounted a threatening attack at the other end, the ball was spilled and the Tigers scrum was penalised for a second time. Loosehead Boris Stankovich picked up an injury and was replaced by Marcos Ayerza, but not before Saints were awarded yet another penalty at the breakdown.
Myler's kick was on the mark from fully 50 metres to give Saints a 6-0 lead after 11 minutes but Leicester then strung together a series of threatening attacks. Again they yielded penalties rather than tries but Ford was equal to the task and pulled his side level with two successful kicks.
The two fly-halves exchanged penalties again to take the score to 9-9 after 24 minutes, but that was no real reflection on either side's willingness to move the ball through the hands.
Leicester were seeing rather more of the ball, however, and deservedly went ahead when Mafi barged past Vasily Artemyev to score in the left corner on 26 minutes.
The rangy flanker had begun the attack by fielding a restart on his own 22 but the telling thrust had been delivered by Billy Twelvetrees, carving through the Saints defence with Graham Kitchener in support. Ford added the conversion.
Scrum-half Martin Roberts prevented further damage by being first to a dangerous grubber kick by Murphy, at the cost of a five-metre scrum.
Although the Tigers' front row was now more than up to the challenge posed by Tonga'uiha and Co and drove menacingly to force a penalty, Ford spoiled his unblemished record by missing the relatively easy kick.
Saints approached the second half with far more purpose but again collapsed a scrum and this time Ford converted his penalty from 50 metres to open up a 10-point lead.
John Downey and George Pisi nearly fashioned an opening but the ball was spilled within striking distance of the Tigers' try-line.
Two minutes later Myler tried to force an opening with a floated pass that only found its way into the hands of left wing Hamilton who raced from his 22 to score at the other end. Ford converted the 50th minute try and Leicester were three scores ahead.
It made the decision to spurn a kickable penalty on the hour all the more puzzling as Leicester then successfully defended a line-out in the corner and then a series of five-metre scrums.
Five minutes later, Ford left the field to be replaced by Flood as the Tigers' coaching team decided they needed the England man's experience. The youngster had again shown remarkable maturity and kicking prowess.
The penalty count against them was mounting, however, and in the 71st minute skipper Murphy was shown a yellow card for his team's repeated infringements.
But it was not until the 75th minute that Saints' desperate attacking efforts were rewarded when Day crashed over in the corner for an unconverted try.
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