CD Stag Greg Hay was 93 not out at No 3 while Jayden Lennox (43 runs) and Josh Paerau (38) added to the cause.
"Our fielding was very poor and we dropped a lot of catches," Sinclair lamented, claiming Senarathne benefited from the whoopsies five times.
In the run chase, NOBM were 154 all out with Sinclair 90 (152 balls) and No 8 Daniel Drepaul 16 (82) the only ones digging their toes as the rest came and went.
Stevie Smidt took 4-42 but Jeremy Kuru (2-13) and Lennox (2-19) were the most frugal with the ball.
At Taradale Park, Havelock North CC lost the toss but made hay with 318-5 in 55 overs on the way to an outright victory.
No 3 Graeme Tryon scored 155 runs, including 20 boundaries and six sixes.
Opener Ben Fair anchored the innings with 71 runs to take it to the 52nd over.
In chasing the target, Sharpies Driving Range Taradale CC were skittled for 175 runs in 38.4 overs.
No 4 Luke Kenworthy 80 (99) was the mainstay of the hosts with No 7 Luke Donaldson adding 34 from 26 balls.
Tryon took 4-19 while Sahil Bogal took 2-46.
"Sahil bowled really well but we had lapses on the field with dropped catches," said Havelock North captain Jared Priest.
"We're just really happy to make it two in a row after a tight one against Cornwall last weekend," Priest said, hoping for another against NOBM this Saturday.
At Cornwall Park, Hastings, Ruahine Motors Central Hawke's Bay won the toss and padded up for a respectable 206-9 in 55 overs.
Opener Will Harker scored 42 runs while No 8 Blair Tickner was unbeaten on 39 after the visitors had seven batsmen getting into double figures.
Spinner Jono Hall claimed 3-38 while Charley Crasborn took 3-34.
A depleted Heretaunga Building Society Cornwall CC were 172-9 off 53 overs with No 6 Hall scoring a quick-fire 60 from 65 balls while opener Scott Brocklehurst made 36.
CHB quickie Charlie Robson took 3-28 in their outright defeat.
"We had an eligibility issue with a young fellow about 10 overs into the game," said Cornwall player Graeme Hodges after someone pointed it out to them.
With a few university players returning in the next couple of weeks, Hodges said they would see how they fare in the nets before herding them into senior or premiership squads to boost numbers.
