For the first time in three weeks the Saints were the ones conceding an early score, not scoring it. Although the visitors had their fair share of ball in the opening few minutes - including a great break from Soane Tonga'uiha from a ruck - they could not get out of their own half in the first few exchanges as the Ospreys pegged them back.
As with their Round 1 trip to Exeter the Ospreys' fulcrum was Matthew Morgan. The slight fly half belied his stature by regularly asking questions of the Saints defence, although it was his boot that opened the scoring with a fourth-minute penalty.
Saints had their chance to reply through Ryan Lamb four minutes later, but although his 40-metre penalty dropped inches wide of the left-hand upright there were already some promising signs for the visitors.
Vasily Artemyev had made a dangerous run down the left and Chris Ashton was being brought into the action regularly. One pass from Dylan Hartley was ruled forward, while the wing's chip ahead pushed the Ospreys back to their own line.
However this pressure was not converted into points and when the Ospreys next visited the Saints' 22 Morgan showed them how it was done by landing his second penalty.
The Ospreys may have been getting the points, but it was the Saints who were asking the questions with their power, pace and off-loading game. Had Scott Armstrong found the supporting Armetyev on his outside following one good run then the Russian could have had a decent run at the line.
He would not have to wait long for his first chance, but while there was plenty of running rugby to excite the Bridgend crowd, what really brought them into life was the physical stuff up front. Neither side was taking a backward step, with home lock Ian Evans earning a talking to for shoving Ashton in the back.
Referee Neil Hennessy seemed to have made his opinions clear. But not clear enough for Evans's second row partner, Tom Smith, who saw yellow barely 60 seconds later.
Saints had a man advantage up front, but it was the men out wide who made the most of it, Ben Foden putting Artemyev over unopposed in the 21st minute. Having defended a lineout drive reasonably well the Ospreys midfield rushed up, and with Lamb spotting his strike runners in open space and flinging an over-the-top pass the score was a formality. The conversion attempt was not so straightforward, but it sailed over nonetheless and with Lamb's earlier penalty the Saints were ahead for the first time.
They may have been making the running, but the visitors were not having everything going their own way and when Smith returned to the field his team had reduced the deficit to just the one point courtesy of a Morgan penalty from halfway.
A fourth success from the tee put Ospreys back in front, and had centre Ben John's hands not failed him at the vital moment he would have been away in the clear. Another aspect of their play that was failing the Pro 12 leaders was their discipline, and when scrum-half Tom Habberfield became the second Osprey to find himself in the sin bin Saints found themselves a man up once more.
This time however the Ospreys not just held out what was being thrown at them, but landed a sucker punch through Sonny Parker, who intercepted an Artemyev pass to run in from 60 metres. Morgan's conversion made it 19-10 and the hosts had a rousing send-off as they went into the half-time break.
But within two minutes the Brewery Field fell silent when Dylan Hartley found himself at the bottom of a ruck for his first try of the season. The score came from a fumbled kick off and some immense power from the Saints scrum. This had earned a lineout and while the drive took some time to put together the patience was rewarded with the try.
Six minutes later the Saints were back on the home line, courtesy of some great running from the back three. Once again the pack inched their way forward, only to be stopped by referee Hennessy, who ruled that a ruck had been deliberately turned into a maul and allowed Morgan to clear his lines.
There was no such mistake in the 55th minute. Again the roots of the score were from the scrum, this time a win against the head. James Downey was forced into touch, but Habberfield's box kick from the lineout headed straight up and down, and with a number of Ospreys offside Lamb kicked for the corner.
Again the drive inched forward, and again Hartley was the beneficiary - albeit following plenty of consideration from TMO Gareth Simmonds. There was no such debate about the next score, Calum Clark crossing unopposed after collecting a Lamb cross kick, and with both conversions bisecting the uprights the visitors had turned a five-point deficit into a 10-point lead in the space of 150 seconds.
There may have been a bonus point in the bag, but the win was still a long way off as the Ospreys fought to get themselves back in touch. Morgan's fifth penalty helped this immeasurably, and there was certainly fortune on the Saints' side when James King's break was pulled back for a forward pass.
The scrum had evened up, too, but although Ospreys were winning penalties they were making mistakes at the subsequent lineouts, where Samu Manoa's handling and awareness were proving very useful.
The home side also had a great chance to tie things up when John crashed through the midfield. The break was spoiled when the centre held on in the tackle, and there was an equally questionable choice from his opposite number Armstrong at the other end of the field, who opted to go for the line himself rather than use either of the unmarked men outside him.
Instead the game clinching score belonged to Stephen Myler, his last-minute penalty securing a 10-point final margin.
REFEREE Neil HENNESSY (WRU)
4mins OSPR Pen Morgan 3-0
8mins SAINTS Miss pen Lamb
13mins OSPR Pen Morgan 6-0
16mins SAINTS Pen Lamb 6-3
20mins OSPR Yellow card Smith
21mins SAINTS Try Artemyev Con Lamb 6-10
27mins OSPR Pen Morgan 9-10
32mins OSPR Pen Morgan 12-10
35mins OSPR Yellow card Habberfield
40mins OSPR Try Parker Con Morgan 19-10
HALF-TIME OSPREYS 19 SAINTS 10
42mins SAINTS Try Hartley 19-15
55mins SAINTS Try Hartley Con Lamb 19-22
57mins SAINTS Try Clark Con Lamb 19-29
62mins OSPR Pen Morgan 22-29
80mins SAINTS Pen Myler 22-32
FULL-TIME OSPREYS 22 SAINTS 32