Winger John Kotze ran a incisive line off first-five Tim Blundell's shoulder and crossed under the posts.
Blundell's prodigious right boot came to the fore in the first half, finding touch with raking right footers.
Mid Western's midfield combined well early.
Centre Dan Wells provided robust defence while second five Kaitiana Vette-Walsh was a constant threat with ball in hand.
Vette-Walsh made a break soon after their first try and got Mid Western back in enemy territory.
A penalty in the ruck followed, giving Mid Western an easy three points through Blundell.
Mid Western continued to dominate the contest in the middle of the first half.
While they couldn't convert on their opportunities, they seldom allowed Waipu a glimpse into attacking territory.
Waipu finally got on the scoreboard during a rare foray into the Mid Western 22.
An intercept from the Waipu hooker almost resulted in a try, but Mid Western winger Ceejay Taylor-Mackie chased him down and forced a knock-on five metres out.
Mid Western then conceded a free kick off the scrum.
Waipu worked the ball wide to find lock Matt Abraham, who scored out wide.
Abraham was in for his second five minutes later after quick thinking from halfback Louie Ward spotted a chance to take a quick tap.
Ben Mathers converted from out wide to give them their first lead of the game.
It was short-lived though as Blundell hit a left-foot drop goal on the stroke of half time to hand Mid Western a 13-12 lead.
Waipu coach Mark Wells gave his side a bit of a spray during the break but the message didn't sink in early in the second half.
Waipu gifted Mid Western prime territory after an errant kick that drifted out on the full.
Flanker Grayson Thyne crashed over by the posts, giving Mid Western an eight point buffer.
Waipu hit back with a penalty shortly after but it took a fortuitous bounce to hand Waipu momentum.
Mid Western failed to give clean ball to halfback Brad Crosbie, who then passed the ball behind the backline.
Waipu's midfield combination saw an opportunity.
Second five Chance Gray gathered the ball on halfway and offloaded to centre Erenimo Tau, who crossed over for a try.
Mathers hit a tough conversion to give them a lead they would not surrender.
After getting another penalty, Waipu camped in opposition territory and added to their lead when Halse ghosted through the defence.
Another penalty from Mathers gave Waipu breathing room, and Tau topped off a dominant second half effort with a 90 metre intercept try.
Mark Wells was happy with the second half effort after a tough first 40.
"We owned the breakdown in the second half after being outmuscled on both our ball and their ball in the first," he said.
"The guys flipped the switch in the second half and gave us what we asked for."
Mid Western coach Danny Woodcock lamented his side's errors after a great first half.
"Two intercepts and handling errors let us down. Three of their tries were directly off our mistakes," he said.
"We stuck to our game plan in the first half, but credit to Waipu for their efforts in the second."
Mid Western take on table-topping Mid Northern next week. Waipu travel to Kamo.
