The pair put on 145 for the fifth wicket - twice as many as any other Auckland partnership - but let themselves down late in the day.
First Cachopa (79) was bowled by Luke Woodcock, then de Grandhomme (86) suffered a similar fate from the bowling of Mark Gillespie six overs later. Their departures saw Auckland reach 280-7 at stumps, leaving the tail with some work if the visiting side are to make up the 119-run gap.
Elsewhere, top-of-the-table Canterbury are in a strong position following two days of their visit to Dunedin to play Otago. After Matt Henry took five wickets to help dismiss the hosts for 200 in their first innings, Canterbury capitalised on their 80-run advantage.
Peter Fulton (10) failed for the second time in the match but another half century from Tom Latham, along with an unbeaten 42 from Rob Nicol, saw Canterbury head to stumps ahead by 260 runs with four wickets in hand.
The match between the competition's two bottom teams is set for an intriguing conclusion tomorrow, with Central Districts making a mess of a meagre chase against Northern Districts in Napier.
After rolling the Knights for 139 in their second innings, CD were set just 70 for victory but Scott Kuggeleijn took three late wickets to leave the hosts on 14-3.