ICC Women's World Twenty20, Taunton
Group A: New Zealand 127-1 beat Australia 123-8 by nine wickets
Group B: Sri Lanka 105-6 beat Pakistan 104-7 by four wickets
Australia were on the back foot after Ruck's impressive spell
Aimee Watkins and Suzie Bates shared an unbroken stand of 118 as New Zealand's women breezed to a nine-wicket World Twenty20 win over Australia at Taunton.
Australia could only muster 123-8 after slumping to 25-4 at the start of their innings, with Sian Ruck taking 3-12.
Lucy Doolan fell cheaply at the start of New Zealand's reply but skipper Watkins made light of the run-chase.
She hit a six and 12 fours in her 73 off 51 balls and Bates made 41 as they reached 127-1 with 20 balls to spare.
Australia went into the game with every reason for optimism, having beaten hosts England in a warm-up game.
But their confidence was badly shaken when Ruck bowled Leah Poulton and then sent back Lauren Ebsary for a first-ball duck when she won an lbw decision.
Shelley Nitschke (18) became Ruck's third victim when she was caught behind by Rachel Priest and Australia could ill afford the run out of Jodie Fields for three.
Captain Karen Rolton could only manage six before she was bowled by Kate Pulford but Lisa Sthalekar collected seven fours in her 46 off 36 balls to at least give the bowlers something to defend.
Needing early wickets, Australia picked up one when Poulton ran out Doolan with only nine on the board.
They could not add to that success, however, as Watkins and Bates produced some superb batting to post the second-highest partnership in a women's Twenty20 international.
Ellysse Perry conceded 31 from her three overs and Sarah Andrews did not fare much better as the pair saw New Zealand home to emphatic victory.
In the day's second match, a terrific bowling performance from Sri Lanka's 25-year-old medium-pacer Eshani Kaushalya restricted Pakistan to 104-7 and helped set up a straightforward win.
Kaushalya was the last of six bowlers to appear - but took 3-16 from her four overs. Sri Lanka reached their target in the 17th over of their chase, losing six wickets along the way.
The tournament comprises two groups of four with the top two qualifying for the semi-final stage.
All the group games are being played at Taunton, with one semi-final at The Oval and the other at Trent Bridge. The final takes place at Lord's on 21 June.