And there was further bad news for the home crowd as Mark Anscombe said he feared that Irish winger Tommy Bowe could be out of action for some time after suffering what seemed like a serious knee ligament injury in the closing stages.
"We need to have him scanned to establish the scale of it but it looks serious. We will find out more after the scan and see how long he will be out," said Anscombe.
He had few complaints that their superb 13-match winning run came to an unlikely end.
"We created enough chances to win it, but we didn't have the composure to take the scores. They started well with ten points in the opening 18 minutes and we didn't take our chances. We were beaten by the better team," he added.
Ulster had a chance to win it two minutes from time but Ruan Pienaar's penalty from the right touchline narrowly missed the target as Ulster fell to their first loss under Anscombe.
The coach had sent out a word of warning after their last three Pro12 games as he felt their form was dipping despite the continuance of the winning run. His worst fears were realised as Saints dug deep to carve out a deserved victory against an Ulster side who never looked capable of reaching the heights of last week's five-point haul in Franklin's Gardens. The net result is that Ulster could now find themselves heading to Castres needing a result – having never won a competitive match in France before.
Northampton set out their stall early but while they dominated the early moments, a possession stat of 80 per cent after 10 minutes still only yielded a 3-0 lead. And that came from an Ulster mistake when Northampton piled on the pressure after an overthrow from Rory Best, but they had to settle for a penalty from Stephen Myler after the home defence held firm.
However, Northampton continued to dictate proceedings and they got their reward after 18 minutes, working the ball through hands from the left inside the '22' for Ken Pisi to set up his No 8 Gerrit-Jan van Velze and the South African fended off Andrew Trimble to dive over. Myler landed the touchline conversion to make it 10-0. Northampton lost van Velze after 26 minutes to a head injury picked up scoring the try, paving the way for Courtney Lawes to enter the fray. A couple of penalties from Paddy Jackson were all Ulster had to show for their efforts as they went in 10-6 down at the break.
Jackson gave Ulster a further boost two minutes after the restart when he made it 10-9 with his third penalty. Northampton responded to the challenge superbly and it took some frantic defending by Ulster to keep their line intact.
It was clear that Ulster's four-year unbeaten run in the Heineken Cup at Ravenhill was under serious threat by a rejuvenated Saints side. Mark Anscombe responded by drafting in Craig Gilroy for Trimble on the left wing. Ruan Pienaar then had a chance to try edge them in front for the first time but a trademark penalty from inside his own half landed just short of the posts.
With just three minutes remaining, Ulster got a great chance when a break from Bowe yielded a penalty on the right. Bowe was forced to go off and after a delay of several minutes Pienaar lined up the kick from the right touchline but narrowly missed the target and Northampton cleared their lines.
Scorers – Ulster: Jackson 3 pens. Northampton Saints: Van Velze try Myler con, pen
Ulster: J Payne; T Bowe (N McComb 77), D Cave, P Wallace (L Marshall 68), A Trimble (C Gilroy 56); P Jackson (P Marshall 62), R Pienaar; T Court (C Black, 68), R Best, J Afoa; I Henderson, D Tuohy (R Lutton 79); N Williams (R Diack 71), C Henry, R Wilson
Northampton Saints: B Foden; K Pisi, G Pisi, T May, J Elliott; S Myler, L Dickson; S Tonga'uiha (A Waller 63), M Haywood, P Doran-Jones (B Mujati 54); S Manoa, C Clark (M Sorenson 64); T Wood, P Dowson, G van Velze (C Lawes 26)
Referee: N Owens (WRU)