Freeman's unstoppable display inspired Northampton's six-try masterclass, with Bath only able to touch down three times in response.
Henry Pollock, an England team-mate of Freeman, bagged two tries and Archie McParland got the other to complete the rout.
Thomas du Toit nabbed two tries for Bath and Tom Dunn also scored.
It was second-placed Bath's first home defeat since losing to La Rochelle in the European Champions Cup on December 6, 2024.
The hosts did not even manage a bonus point as their end of 11 consecutive home wins came to an end.
Third-placed Bristol hit back from a 10-point deficit and shrugged off a late red card for Joe Batley in their 36-27 win over Newcastle at Ashton Gate.
Newcastle led by 10 points early in the second half, but Bristol's introduction of Ellis Genge turned the game.
Bristol scored six tries, two from Louis Rees-Zammit, with Matias Moroni, Gabriel Oghre, Noah Heward and Kaveti Ravouvou also touching down.
Tom Jordan added two conversions and James Williams kicked one.
Newcastle secured their first league point of the season with four tries of their own.
Oli Spencer scored two and Murray McCallum and Ollie Leatherbarrow bagged the others, while Brett Connon kicked a penalty and two conversions.
Saracens ended their run of three successive Prem defeats as they defeated Gloucester 30-21 at Kingsholm.
Theo McFarland scored two of Saracens' four tries, while Theo Dan and Ivan van Zyl also touched down.
Owen Farrell kicked two penalties and two conversions as Saracens strengthened their play-off push.
Gloucester had first-half tries from Freddie Thomas and Arthur Clark, plus a late Will Knight effort, with Ross Byrne converting all three scores, but they slipped to a seventh loss in eight league matches this term.