Hosts England beat Ireland by four wickets, but their victory was overshadowed by an injury to Nat Sciver-Brunt.
England captain Sciver-Brunt was forced to retire from the match on 48 with "tightness in her calf".
Sciver-Brunt only returned from a torn left calf last week, but after leading England's recovery from 35 for three, she limped off with nine runs needed to win.
England reached their meagre 119 target with 15 balls to spare to move on to four points in group B and put themselves in pole position to reach the semifinals.
England's Charlie Dean said: "I think it was just tightness. Credit to Nat, she just took herself off as a precaution to avoid any further damage."
Sciver-Brunt has just four days to recover before England are next in action against Scotland at Headingley.
England bowler Sophie Ecclestone earned player of the match honours for her impressive spell of 3-22.
IRELAND: Amy Hunter (w), Alana Dalzell, Gaby Lewis (c), Orla Prendergast, Rebecca Stokell, Leah Paul, Alice Tector, Louise Little, Arlene Kelly, Cara Murray, Aimee Maguire.
ENGLAND: Amy Jones(w), Danni Wyatt-Hodge, Nat Sciver-Brunt(c), Alice Capsey, Heather Knight, Freya Kemp, Danielle Gibson, Charlotte Dean, Sophie Ecclestone, Linsey Smith, Lauren Bell.