Cardiff’s problems began when Lomu spilled the ball under no pressure, allowing the Reivers to sweep up field. Lock Scott MacLeod could have reached the line himself but unselfishly unloaded to McGee, who was left with a stroll. Hore added the extras.
Cardiff hit back positively to repair some of the damage with a simple penalty by Nicky Macleod. But Hore replied in identical fashion to restore the advantage for the hosts.
Lomu earned a ticking-off from referee Alain Rolland for thumping rookie Garry Law with a late challenge.
There was still time for Hore to complete his penalty hat-trick and give his side a 13-point cushion.
The rattled Blues came out with more urgency after the restart and eased the jitters with two penalties from Macleod. Cardiff set up camp in the 22-zone but found the Borders defence in mean mood and could not make the breakthrough.
Having weathered the storm, the Reivers created a fine second touchdown. Danielli came into the line in midfield to provide the time and space for Stuart Moffat to send Nikki Walker over. Hore again converted - then banged over another penalty.
The Blues refused to buckle, however, and an opportunist try by Aussie centre Marc Stcherbina - converted by Macleod - ensured a tense finale. There was more drama in stoppage time when old stager Craig Quinnell grabbed another touchdown.
: Borders: Tries: McGee, Walker. Cons: Hore 2. Pens: Hore 4. Cardiff Blues: Tries: Stcherbina, Molitika. Cons: Macleod 2. Pens: Macleod 3.
: MacRae, Danielli, MacDougall, Law, Walker, Hore, Cusiter, McGee, Ford, Douglas, MacLeod, Palepoi, Brown, Sititi, Miller. Replacements: Moffat for MacRae (23), Parr for McGee (60), Scott for Ford (71), Stewart for Palepoi (71), Dalziel for Miller (55).
: Morgan, Czekaj, Stcherbina, Davies, Lomu, Macleod, R. Powell, Yapp, Goodfield, B. Evans, D. Jones, Goode, Molitika, Schubert, Sowden-Taylor. Replacements: Dewdney for Czekaj (61), L. Thomas for Davies (69), W. Evans for R. Powell (75), Quinnell for D. Jones (69), Lewis for Schubert (69).
: Alain Rolland (Ireland).