Ben Blair kicked two penalties either side of Jason Spice’s first-half try before Cardiff’s defence secured a famous win.
The victory sends the Blues marching to Twickenham for next month’s Anglo-Welsh showdown against Gloucester – the first cup final in the region’s six-year history.
This result also made sure Wales still have interest in this competition after the Ospreys were defeated in the first of these back-to-back semi-finals at Coventry’s Ricoh Arena.
The Blues knew Welsh hopes rested on their shoulders and they got a dream start when Blair punished Dylan Hartley for conceding a penalty after just 45 seconds with the game’s opening points to settled any nerves.Â
But any fears the Blues would take a safety-first approach were swiftly quashed as they looked to break from their own try line in the opening minutes.
But Cardiff’s high tempo style also came with risks and they were lucky to escape as Northampton blew a series of half chances. Stephen Myler and Blair both sliced shots at goal, but after half an hour, the Blues finally grabbed the game’s opening try.
Wales centres Tom Shanklin and Jamie Roberts were the catalysts, Gethin Jenkins and Xavier Rush weighed in before Spice scurried through a hoard from close range. Blair missed the extra points but the Blues held onto the 8-0 lead until half-time.
Any thoughts of building on the advantage were wiped out just 80 seconds into the second half when Joe Ansbro crashed over in the corner. That shocked the Blues back into life with wings Halfpenny and Tom James causing havoc in the Saints defence. But the Blues lacked the final touch as Blair missed a second shot at goal.
Saints had similar problems, missing three kicks, before Blair opened a six-point lead that the Blues defended for the lives for the final nine minutes.
