Steven Croft took a brilliant catch off his own bowling to dismiss Jamie How (21), while some sharp keeping from Foster saw the end of Matthew Sinclair (13).
Halfway through their innings the Stags were four for 49 and in need of a substantial partnership.
Following a 30 run fifth wicket stand with Cachopa, captain Kieran Noema-Barnett was then caught on 15 to bring debutant Will Young to the crease. The 20 year-old made his way to five before being run out in the 17th over.
Cachopa though was beginning to look comfortable and picking up boundaries at ease. Three sixes in seven balls lifted him to his half-century in the 18th over, with the milestone coming off 28 balls.
He continued to work in fours and sixes and after twenty overs had inspired his side to a total of 149 for six.
Croft picked up two wickets in his two overs for 12 runs, while Anton Devcich was economical with his four overs going for just 15 runs, as well as dismissing Noema-Barnett.
The next HRV Cup match is next Friday night when the Knights host the Canterbury Wizards.
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Points table
Northern Knights 8
Auckland Aces 4
Wellington Firebirds 4
Central Stags 0
Otago Volts 0
Canterbury Wizards 0
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