The Cats, under the tutelage of Springbok assistant coach Tim Lane, were outscored by five tries to one, after they took an early lead through a try from Bok wing Friedrich Lombard.
New Cats fly-half Kennedy Tsimba, who is trying to get clearance to play for South Africa from the IRB, missed the conversion, but added a penalty just minutes later.
The Saints Select XV hit back with a try from Oriol Ripol, but Bruce Reihana, a former Super 12 star for the Chiefs, missed the conversion to leave the half-time score at 8-5 in the visitors' favour.
The Cats began the second half rather nervously with a knock-on from Tsimba giving the Saints XV a scrum on the South African team's line. The Saints scrummed strongly and eventually prop Chris Budgen burst over from a ruck for a score, which Reihana converted.
Budgen collected his second try soon afterwards, which Reihana also converted, suddenly putting his side ahead by 19-8.
Lane then began using his bench, allowing Test Boks James Dalton, Bob Skinstad – the Cats' skipper for 2003 – and André Pretorius a run, but they could not prevent further tries from centre Mark Tucker and former England fullback Nick Beal.
Reihana kicked both conversions, giving his side a massive 25-point winning margin against a side expected to make an impact at Super 12 level later this month.
The Cats open their Super 12 campaign against perennial strugglers, the Bulls, on Friday, 21 February in Bloemfontein.
For the Saints Select XV:Tries: Ripol, Budgen 2, Tucker, BealCons: Reihana 4
For the Cats:Try: LombardPen: Tsimba