City's opener Callum Gegg was their top scorer with an important 42 before Kaipara spinners Michael O'Flaherty and Luke Beaven turned the screws on the City batsmen, making it hard to score on what was a well-used Cobham pitch.
Both bowlers picked up two wickets, going for under five an over off their four overs.
In their innings, Kaipara started badly with captain Rory Christopherson run out by his opposing skipper in a tight call in the third over. From there, Kaipara struggled to form any partnership of substance with No 3, Kyran Dill, top-scoring with 29.
Tight bowling from Gegg and opener Stacy Hyndman, who both picked up three wickets, and golden ducks for two of Kaipara's middle order batsmen enabled City to control the game and have Kaipara all out for 106 with one ball left in their innings.
Darkins said having scoreboard pressure in a final was always going to play to City's advantage.
"We knew if we bowled well and put them under pressure, we'd give ourselves every chance which we managed to do."
Darkins credited his side's effort in the field, hanging on to some impressive catches in the deep and working hard to reduce the runs Kaipara batsmen found in Cobham's large outfield.
Kaipara skipper Christopherson said the game was always going to be hard to win after they lost the toss, but credited City's bowlers for how they strangled his batsmen for runs.
"Despite not having any recognised spinners on a pitch that would absolutely suit that, it tells you a bit about how their seamers bowled and managed to defend 123."
He said this would give his side extra motivation to continue their good form in the 50-over competition and secure a home final after the last game of the competition this weekend.
In the reserve grade final held on Sunday morning at Cobham, Maungakaramea beat Bream Bay, chasing down their opponent's 117 with six overs to spare, David Heappey top-scoring for Maungakaramea with 38.
In Saturday's round of premier 50-over matches, Kaipara, City and Maungakaramea all recorded victories in the penultimate round of the competition.
Kaipara chased down Whangārei Boys High School's score of 93 all out at Kensington Park. Four of Kaipara's bowlers took two wickets each, restricting their opposition to the low total, which was chased down in 18 overs.
At the Maungakaramea Domain, Onerahi couldn't defend their score of 123 against Maungakaramea after the home side chased it down in just under 38 overs with four wickets down.
Despite Onerahi's Fletcher Coutts scoring a run-a-ball 64, Maungakaramea bowler Chris Page took five wickets in a row with the visitor's score at 44/4, leaving Onerahi with little chance of victory.
City would go on to make it two wins from the weekend as they chased Kamo's 135 at Cobham Oval in 33 overs. Kamo were on the brink of collapse at 59/8 before Nos 10 and
11 Nathan Parkes and Matt Kingi scored 17 and 32 respectively and got their side to a somewhat defendable score.
However, City got to their target with relative ease, losing just three wickets with Stacy Hyndman, who took three wickets in the first innings, returning with the bat to score a match-winning 47.
Kaipara and Maungakaramea are tied at the top of the table with one round left.
On Saturday, Kaipara play Onerahi at Kensington Park, Maungakaramea take on City at Maungakaramea Domain and Kamo play WBHS at Kamo Recreation Ground in games which will decide who will host the final on February 17.
