Jack Manix-Geeves and Tom Garwood strode to the wicket of Riverside No.1 as the Blues looked to make a statement against the reigning premiers Launceston.
Launceston's Jackson Miller (3-48) sent Garwood on his way early with an edge to the returning Alistair Taylor to give the Lions an ideal start.
Coming in at second change, Miller also picked up Blues' first-drop Matthew Kerrison and Patrick Mackrell to leave Riverside looking vulnerable at 4-65.
Arguably the pick of the bowlers was Lions' leg-spinner Will Bennett (1-20 off 10) who managed to confound the Blues batters with his turners.
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His economical spell was rewarded in his final over when Aidan O'Connor (36 off 70) edged behind to Taylor when the 15-year-old was looking threatening in the closing overs.
Middle-order pair Ramesh Sundra (48 off 65) and Peter New (17 off 25) built a 51-run partnership, which included crucial power-hitting from Sundra, to enable the Blues to reach a defendable score of 6-178 at the close.
Needing to score 179 at 3.58 an over, Samuel Elliston-Buckley (25 off 41 balls) and Cameron Lynch (66 off 99) built a strong foundation for the Lions chase with a 61-run partnership.
Lynch looked impervious to the Bles bowling as he stroked seven boundaries and one six in an entertaining knock.
The tables turned when Jesse Homan (2-41) breathed life into Riverside's defence when he picked up Lynch and Taylor in succession to have the Lions at 3-124 in the 33rd over.
Despite going wicketless, Blues' skipper Garwood (0-16) proved miserly with the ball from his allotment to help Riverside drag the Lions deep into their innings.
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Returning Raider O'Connor (4-25) knocked over Miller and had Tom Gray edging one to New to leave the Lions' on shaky ground at 7-152, before the Blues claimed the final few Lions wickets.
"Aidan had some really simple plans and he was the only one who executed them today and seek the rewards of that, he did really well, he's growing in confidence each week," Garwood said.
That was soon extinguished when O'Connor had Dean Thiesfield (16 off 37) caught and Sundra knocked over Bennett (2 off 11) to give the Riverside their second victory of the season.
"A lot of work to do, we didn't play our best cricket today and we still haven't played that yet, we've got a lot of belief and we executed our plans late," Garwood said.
After looking in good touch last round, Sisitha Jayasinghe (72 off 111) cashed in at the top of the order to propel South Launceston against the Westbury.
Jayasinghe combined well with Mackenzie Barker (40 off 68) for an 85-run partnership to seemingly vindicate the Knights' decision to bat first after winning the toss. The Knights carried their strong start through their allotment, finishing with 7-199.
The Shamrocks were on edge before tail-ender Alex Jordan hit a boundary off the second-last ball of the game to seal a Westbury win. Westbury playing coach Matthew Battle was pivotal to his side's efforts with a half-century in the run-chase.
"Matt had a direct hit run-out and we were able to gain a bit of ascendancy from that and he battled really sensibly, occupied the crease on a wicket that was quiet hard to score on," Westbury captain Daniel Murfet said.
"Getting a win before Christmas is crucial, one-day wins are massive and we're looking to get as many of them as possible, we take that into next week and go again."
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