Cardiff crashed out of the Heineken Cup at Franklins Gardens in a match soured by the late sending off of Northampton prop Mattie Stewart.

Stewart was dismissed for alleged stamping in the closing moments just two days after he was reprimanded by a Rugby Football Union disciplinary tribunal for punching and kneeing an opponent in a match last month.

But while Northampton finished with 13 men after flanker Andrew Blowers was sin-binned, they were still too strong for a Cardiff side that rarely threatened to get the win they needed.

But the Blue and Blacks failed to register a try, while the Saints crossed early in each half to kill off the Welsh side's hopes.

Cardiff could consider themselves fortunate to be only a point adrift at half time after withstanding heavy Northampton pressure in the opening period.

The Saints started off at a ferocious pace with England wing Ben Cohen grabbing a try in the left corner as early as the second minute.

Paul Grayson converted for an early 7-0 lead, but Northampton repeatedly spoiled their good work by conceding penalties and were duly punished by Iestyn Harris.

But Grayson replied with two of his own to edge the Saints narrowly ahead 13-12 at half-time.

Cardiff's hopes suffered a major setback two minutes after the resumption when referee Iain Ramage awarded Northampton a penalty try after a high tackle on centre Peter Jorgenson as he bore down on the Cardiff line.

Grayson converted for a 20-12 lead, and although Harris replied with his fifth penalty, Grayson restored Saints eight-point advantage with another penalty.

The fly-half then slotted a drop goal with the last kick of the match to finish with a 16-point haul.

Northampton: Tries: Cohen. Cons: Grayson 2. Pens: Grayson 3. Drop Goals: Grayson.

Cardiff: Pens: Harris 5

Northampton: N Beal; C Moir, P Jorgenson, J Leslie, B Cohen; P Grayson, J Brooks; T Smith, S Thompson, M Stewart, J Phillips, R Hunter, A Rennick, A Blowers, B Pountney (capt). Reps: S Brotherstone, C Budgen, G Seely, M Soden, I Vass, M Tucker, S Webster.

Cardiff:R Williams; A Sullivan, J Robinson, P Muller, C Morgan; I Harris, R Howley; S John, J Humphreys, D Young (capt), C Quinnell, J Tait, R Appleyard, E Lewis, M Williams. Reps: P Rogers, A Lewis, A Jones, S Sititi, A Booth, N Robinson, M Allen.

Referee:Iain Ramage (Scotland)