After 34 minutes, Leicester was awarded a bonus point for Julian Montoya's attempt.
Gallagher Premiership Northampton: ((5) 26 Tries, Skosan 2, Mitchell and Waller Cons: Grayson 3. Leicester: (27) 55 Try: Nadolo 2. Van Wyk. Montoya. Van Poortvliet 2. Murimurivalu Cons Ford 4. Pens: Ford 3. Drop goal: Ford
Leaders Leicester won their largest-ever victory at Northampton to keep their perfect Premiership start.
Tigers were dominant in the first period. Nemani Nadolo scored two times, as well as scores for Francois Van Wyk and Julian Montoya. Courtnall Skoan's late attempt for Saints was stopped by Courtnall Skosan.
After the break, Alex Mitchell and Alex Waller scored goals for Saints.
Before Jack van Poortvliet's and Kini Murimurivalu's tries, Tigers were able to clear the field with a Ford drop goal and two penalties.
Skosan got a second try towards the end of the second half in front of a sold-out Franklin's Gardens. He went over with just three minutes to go before Van Poortvliet got his third with 30 seconds remaining.
Northampton remains fourth on the table, while East Midlands rivals Leicester are nine point clear at the top. Harlequins are second with two games remaining.
Northampton's errors in the first half matched the Tigers' ruthlessness. Ford's penalty early on was increased by Nadolo's opening, the Fijian international moving over on the left wing following a looping Dan Kelly pass.
George Ford, who was not in the England squad, played an important role in Leicester's win with his leadership and kicking.
Kelly provided the second, leaving four Saints defenders behind. He made a trick run to set Van Wyk up for his 19th-minute attempt. Nadolo then ran in from 40m for the third try after Alex Mitchell misjudged a high kick.
After a period of intense pressure in right corner, Argentina's captain Montoya was beaten over. Saints had previously seen Rory Hutchinson miss his chance to locate him with an overlap just two minutes before.
Leicester's discipline was ruined shortly after the half-time break. Richard Wigglesworth, scrum-half, was yellow-carded after a head-on collision and Cobus Wiese was sinbinned in the lead-up to Mitchell’s attempt shortly afterwards.
With 13 men backing them and a partisan crowd at home, Saints rallied to hold Mitchell over the Tigers line.
The Tigers survived, and Ford calmed their nerves with a 41-metre goal drop goal. This was after a Saints dropout 15 minutes into the second half. Waller then bundled over to the left to reduce the gap to 11 points.
Ford, whose all-round kick gave Leicester a great foundation to play from throughout the 80-minute match, landed two additional penalties. Van Poortvliet blocked Rory Hutchinson’s kick and was over with 15 minutes left. Murimurivalu then smashed his way through five minutes.
Skosan was at the end of Grayson's cross-field kick and went in unchallenged. However, there was still time for Steve Borthwick’s men to score as Van Poortvliet, a young scrum-half, intercepted a pass to make it a touchdown and galloped over.
Chris Boyd, Northampton's director of rugby, spoke to BBC Radio Northampton
"We knew it was coming, but we didn’t react to it."
"They dropped to 14 and 13 and we had five chances and took two.
"If we could take another couple of them and make it even, I think it might be a different script. But as it turned out, our poor performance in 30 minutes was too much to climb.
"We didn’t win the collisions, and we didn’t win the balls up in the air. So if you don’t win those, then you’re inviting George Ford, whom I thought was great, to control the games."
Leicester head coach Steve Borthwick told BBC Radio Leicester:
"I thought their attitude and work ethic were outstanding. Their effort was exceptional.
"But what I also said was how can we improve? We don't have to say we won't try, and there are plenty of things you can do better.
"In the last five minutes of the first period, we gave them a chance and that made the beginning of the second part difficult. We made it even harder by reducing the number of players to thirteen.
"Again, I'll be praising the players, their guts, and the spirit that they showed when they were reduced to 13 men. But we can't stay in that situation."
Northampton: Hutchinson; Skosan, Proctor, Dingwall, Collins; Biggar, Mitchell; Waller (capt), Matavesi, Painter, Ribbans, Ratuniyarawa, Wood, Harrison, Augustus.
Haywood, Auterac Hill, Moon Coles, Lomani Grayson, Litchfield are all possible replacements
Leicester: Burns; Potter, Moroni, Kelly, Nadolo; Ford (capt), Wigglesworth; Van Wyk, Montoya, Cole, Wells, Snyman, Chessum, Van Staden, Wiese
Alternatives: Cowan, Leatigaga and Heyes, Greens, Reffell, Van Poortvliet. Hegarty. Murimurivalu.
Referee: Tom Foley, (RFU).