Goals from Susannah Townsend and then Hannah Martin saw Team GB clinch a quarter-final spot, but their 2-0 win sent Ireland out.
Townsend broke the deadlock after six corner penalties, on hand to follow up with a rebound.
Ireland struggled to put pressure on Team GB and after the first two quarters it was Britain who retained the advantage, however slim.
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Early in the third quarter, Martin doubled her side’s advantage after turning in a pass from the right side of the pitch, scoring her third goal of the tournament so far.
With a two-goal advantage, Isabelle Petter was sent off early in the fourth quarter and Ireland had a chance to press for a goal of their own.
Petter was able to return to the field with a little over seven minutes to go. Ireland, making their Olympic debut in the sport, had just four goals to their name coming into the match, and struggled to break through even when Team GB were a woman down, and then had Roisin Upton sent out with a yellow.
The defeat sees Ireland out of contention for the quarter-final stages, while Team GB still have chance to retain their 2016 title.
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