John LeFevre's sparkling return to form wasn't enough to secure Mowbray's first points of the season as Riverside returned to the winners' list at home.
Having scored 11,11, 2 and 0 in his four previous outings this season, LeFevre led the competition's youngest side from the front with 101 in a total of 6-162 from 45 overs.
The former captain-coach and premiership player put on an 80-run stand with Sam Canny and brought up his three figures with a well-timed boundary through backward point.
Chasing 183 for victory after Mowbray's score received the Duckworth-Lewis treatment, Riverside reached 1-80 before young gun Jesse Price (3-18) took career-best figures to leave the match evenly-poised.
It took an unbeaten 43-run stand between Patrick Mackrell (59) and Lyndon Stubbs (13) to see the Blues reach 6-186 in the 39th over.
"It was really good to get a win so hopefully we'll get a little kickstart here," Riverside captain Tom Garwood said.
"We've got a few games we should be aiming to win over the next few weeks so it's a good start for us, the boys played really well today.
"We lost it probably through the middle a little bit with dropping a couple of catches. John batted really well and made a hundred and at the end we tied it back with Patty and Matthew Kerrison (3-11) before the rain came."
Mackrell's match-winning knock featured three sixes - including two in one over - and was his first batting milestone since returning from a four-year layoff.
"Patty's brought a lot of experience back into the side and that's exactly what he can do - he had a plan and he knew he had to be there at the end and he played really well," Garwood said.
"He's been working on areas he can hit the ball and he played that fantastically well today - he knew where his boundary balls were and also he picked up ones and twos so it was really good to see him make a score."
SOUTH LAUNCESTON became the first side to beat Westbury this season, recording a 103-run victory at Ingamells Oval.
Posting an ominous 8-246 on a cold and windy day, the Knights dismissed the home side for just 140 in 40 overs as Graham Donaldson snagged 3-45.
South captain Tom Waller was quick to point out the absence of Dane Anderson, Matthew Battle, Richard Howe and Greater Northern Raiders players from Westbury's best XI, but was happy with the win all the same.
"It's a confidence booster [but] we're not shying away that they had a lot of players out," Waller said.
"We'd expect them next time we play to have a bit of a stronger side, but it's nice to get a win and know that when we play at our best we can match it with anyone.
"And it's nice in the last three games we've got bonus points, so after a disappointing loss in our first game against Riverside we've really stepped it up the last three weeks."
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Earlier, Sisitha Jayasinghe had his way with the Westbury bowling attack, pillaging 88 at the top of the order to secure his highest Cricket North total since joining the Knights last season.
Sean Harris and Anders Bulow (2-24) both made handy 20-odds before Jeremy Jackson worked an impressive 39 not out from number eight.
Kieren Hume was again the pick of the Shamrocks bowlers with 2-25.
"Sisco really set it up for us at the start," Waller said.
"He took the game on from the start and backed himself with pretty much over a run-a-ball for his innings, he got to 88 and then everyone chipped in to help him out."
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