Tempers were frayed as the two packs engaged in a bout of fisticuffs, before Shane Geraghty dribbled his 40-yard penalty along the floor.
Geraghty did give the hosts the lead in the 21st minute with a sweetly-struck penalty but Little, back in the starting line-up, restored parity with a three-pointer from a tight angle five minutes later.
Bath were giving as good as they were getting, with flanker Julian Salvi making a nuisance of himself at the breakdown and Banahan running some searching lines.
But they conceded the match's opening try against the run of play, Ashton hacking through and touching down from 50 yards out after the ball was turned over.
Geraghty failed to convert, while Little missed a penalty two minutes before half-time.
A fired-up Bath went ahead for the first time in the match in the 47th minute when Hape collected Little's pass on the right wing and burrowed over, with fly-half Little adding the extras.
The hole in the Northampton defence was created by another barnstorming run from Banahan, who was lucky to escape a yellow card after a late tackle on Ashton in the 52nd minute.
Geraghty, who produced a mixed display, was replaced by Stephen Myler on the hour as Saints tried to inject some poise and urgency into their back play.
And six minutes later, Banahan was give a straight red card for reckless rucking on Northampton's replacement fly-half.
The away side had a little under a quarter of an hour to hold out, and they managed to pull further clear in the 72nd minute when Little landed a penalty from out wide for 13-8.
But Bath suffered a heartbreaking end to the match when Ben Foden released Jon Clarke, who sent Ashton over in the right corner. Myler converted to seal the match for the hosts.
Northampton director of rugby Jim Mallinder:
"Bath have good players and they shouldn't be down in 11th place. They can play rugby and can be dangerous.
"It was little bit messy out there and I'm happy to sneak it at the end.
"Chris Ashton is on fire at the moment, we always knew he had potential."
Bath head coach Steve Meehan:
"It's difficult to take because I thought we played the better rugby. I'm proud of the performance.
"We had a big week in training and there was a hell of a lot of passion. I think the supporters should be proud of the players.
"It's unfortunate to battle like that and come away with only one point when you deserve four."
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