Fannin even managed a coveted hattrick, combining a sharp catch from keeper Jeremy Guy with two lbw shouts to bring up his five-wicket bag.
Maungakaramea's innings ended on 133, with Fannin recording figures of seven for 22 from 10.4 overs.
This left City a chase of 93 to secure the win and pole position on the ladder.
Openers Bert Horner (60 not out) and Joey Yovich (23) made sure there were no issues as they romped home, only losing Yovich in the reply.
City's nearest rivals, Onerahi Central, suffered a tough loss to Kaipara Flats which leaves them a tough ask to take out the competition.
Kaipara Flats started day two on 42 for three, holding a 95-run lead, but Onerahi soon swung the match in their favour with three quick wickets.
Pankaj Kumar (58) then rescued Kaipara Flats, with the help of the lower order, to help them reach 177, giving Onerahi a target of 231.
Fletcher Coutts (3 for 28) and Tom Herman (3 for 43) were the pick of the Onerahi bowlers.
In reply, Onerahi struggled early as Shaun Beamish (5 for 56) took the first four wickets of the innings.
Coutts was joined by Kurt Benney (26) and they began a surge at an unlikely victory.
Coutts showed an array of breathtaking shots in his 121-ball 122, belting eight fours and seven sixes as he urged his team closer to the title.
Unfortunately he couldn't quite pull his side over the line, being the last wicket as Onerahi fell seven short of victory.
The final match between Kamo and Whangarei Boy's High School ended up being very one-sided as WBHS cantered to a victory by an innings and 51 runs.
WBHS started the day on 231 for seven, with Cullen Lowe (70) and Kurt Oldridge (19 not out) helping the side to 304 all out.
Kamo's Sean Daniels managed to grab four for 91 with the ball.
Kamo faced a tough ask to even make WBHS bat again and they started inauspiciously, losing both openers for ducks.
Lowe (4 for 52) carried on his fine individual performance to grab four for 52, making life tough for the home side.
Shane Burton (51 not out) and Leon Cross (38) tried their best but ultimately Kamo could only manage 144, leaving them another heavy defeat.