Five penalties from Stephen Myler and May's late effort, sealed a nail-biting 18-14 victory as Saints added to their wins over Gloucester and Exeter - ensuring Jim Mallinder's side continued their 100 per cent record, but they lost Ben Foden to a nasty-looking ankle injury.
It was the end of their opening run of wins for Bath, and they had to make do with a losing bonus point despite the best efforts of the impressive Nick Abendanon and the left boot of Olly Barkley.
Roaring out of the blocks
Bath came roaring out of the blocks and found themselves 5-0 to the good after less than two minutes as a clever grubber kick from Tom Biggs released full-back Abendanon, who chased through to touch down.
Barkley missed the conversion however and Northampton were quick to regroup and Myler was able to capitalise on some strong forward play to notch his first penalty of the night on seven minutes and trim the deficit to two. Barkley then made up for his earlier miss and restored Bath's five-point advantage on ten minutes, only for Saints to grow in dominance as the half wore on.
Myler, who got the nod ahead of Ryan Lamb at fly-half, was showing impressive accuracy from the tee and three more penalties - as Bath continued to show indiscipline - before half-time gave Saints a 12-8 lead at the break.
He picked up from where he left off soon after the restart and was on target with penalty number five on 52 minutes, but Barkley dragged his side back to within four soon after.
Myler was then handed two chances to extend Saints' lead but was wayward at both penalties as the consistency he had shown in the first half eluded him.
Partisan home crowd
Roared on by a partisan home crowd at the Rec, Bath cranked up the pressure and it appeared to have told with 11 minutes left as Saints conceded another penalty, but while Barkley got the accuracy right, he did not have the distance, ensuring the visitors still led by the narrowest of margins.
That miss was to prove costly as, when a Barkley kick was charged down, Northampton raced down the other end and while they were not able to cross for a try, a May drop goal with just over four minutes remaining extended Saints' lead to four.
Back came Bath however and a fine run from Abendanon took them to within striking distance of the try-line and Dominic Day appeared to have made the opening for Barkley but he tried to kick through while there were others better placed outside him.
Sale Sharks visit The Rec. to play Bath on 29th September, whilst the Saints arrive in Salford on 30th November.
Other matches this weekend are: Worcester Warriors v Gloucester on Saturday (1.30pm), Harlequins v Sale Sharks, London Wasps, Saracens v. Leicester Tigers (all on Saturday, 3.00pm). Sunday's match sees London Welsh facing Exeter Chiefs (3.00pm).