Striking a number of fours around the park, his undefeated knock of 63 in combination with another veteran in Gerard Hobbs (22 not out) carried them through to the winning runs by the 22nd over.
After O'Callaghan's initial success, which came when he found his length after being wayward with his first deliveries, neither he nor the other Tech bowlers could trouble the United pair too much further.
Having taken his best bowling figures of 5-15 in nine overs, Power said he was delighted with how well the ball was coming out of his hand, the spinner no doubt looking forward to some more online repartee with United's former strike bowler Andrew Cording.
Now based in England, the aggressive paceman Cording has been on the team's Facebook page expressing his bemused surprise with Power's haul this summer.
"Sixteen wickets so far in the season. If Cords was up to that many, he'd be chuffed," Power smiled.
Batting first, a number of the Tech players got starts but could not score freely as well as Power's success, Hobbs was measly conceeding only 14 runs from his 10.
Tech welcomed back Travis Bartels from university and he got to 20 before falling, with captain Dominic Lock the best scorer with what would have been an unsatisfying 22.
Aside from Power, the other United bowlers shared the wickets, along with one run-out.
Callaghan replied as he bowled three batsman in the space of four balls, before Power came on and through both design or good fortune, began to score regularly behind the wicket.
After O'Callaghan came off, Bartels and Matt Thompson missed their mark a touch, letting Power score boundaries on the off-side, although he did give away a couple of healthy snicks which keeper Kane Watkin couldn't haul in.
Power and Hobbs had recovered the innings at 72-4 after 13 overs, then pushed on to 98-4 by the 18th.
O'Callaghan was back but could not provide another breakthrough, with Power signing the match off with a boundary.
Down at Centennial Park, Matt Burke Engineering Marton Saracens faced a much stronger Bayer Marist outfit than they disposed of at the end of October, but still pulled out a comfortable 90-run win.
Marist had the services of some Wanganui Collegiate players, while NZ U19 squad member Nick Blundell also turned out for them rather than alongside his New Zealand teammate Henry Collier with Saracens.
With a more level playing field, Marton batted through to 253-8, as Collier top scored with 65, followed by Dominic Rayner's 47, with solid supporting hands from Dan Ford (30) and Ben Lewis (30no).
Off his short run-up to go easy on his recovering side strain, Blundell took 2-37 from his 10 overs, while Collegiate's Morgan Inness also got a pair.
In reply, Marist opener Brett Cameron determinedly carried his bat through to 82 not out, including nine 4s and two 6s, but no-one else could stay with him for long enough as they folded in the 32nd over for 163.
The bowlers shared the spoils, with the best being Mark Jones (2-15 from six), Brad Childs (2-5/3) and Collier (2-22/5).
The Hawke Cup game between Active Physio Wanganui and Taranaki in New Plymouth will be played this coming weekend, not today and Tuesday as reported in Saturday's briefs section.
