His 73 from 70 balls included six fours and two big sixes as he found support from the likes of Cullen Lowe (27 off 23 balls) and Isaac Osbaldiston (25 off 16) in their charge towards 250.
There was a lot of fight in the City attack as opening bowler Dwayne Claasen (5 for 49) returned and cleaned up the lower order to give them a chase of 249 for victory.
WBHS were the surprise package last year and they showed they weren't a one-season wonder as they made life tough for the City batting order.
Opening bowlers Sweeney and Caleb Boswell-Smith put City under a lot of pressure and reaped the benefits.
Harry Darkins was the only batsman to surpass 20, as his 37 was the main contribution to their total.
Boswell-Smith was the star of the show with 4 for 39 in a great show of controlled pace bowling.
Sweeney (2 for 17) and Lowe (2 for 29) also chipped in with wickets as WBHS provided a fine team effort.
Vaughn Witten contributed 19 runs but it wasn't enough to stop City being bowled out for 123.
Meanwhile, Onerahi looked in firm control of their match against Kaipara Flats, only for the rain to stop their progress.
After a solid start, Kaipara lost wickets in bunches to be reeling at 107 for 8 after some sublime bowling.
Opening bowlers Tom Herman (4 for 20) and Sean Doel (2 for 20) had classy eight-over stints, Doel being partly responsible for a three-wicket over with two of his own before Ethan Benney knocked the stumps over from midwicket for a runout.
Unfortunately for both sides the weather packed in and no further play was had.
Kamo got themselves in the win column in their season-opener as they beat Maungakaramea by seven wickets.
Tom Lovegrove's 63 led Maungakaramea to 184 as three wickets to Ben Hyde (3 for 25) as well as tight bowling from the rest of the attack made runs hard to come by.
In reply Kamo were rarely troubled as they got to the total, losing just three wickets.
Mark Doegan made 45 before Lakhvir Singh and Hyde scored matching unbeaten 47s to guide their side home.
This weekend sees WBHS travel to Kaipara Flats, Kamo at home against Onerahi and City taking on Maungakaramea.