Porterfield put on 89 with Paul Stirling (42) in the largest opening partnership for Ireland against a top-eight team to set the innings on a sound footing and left his team 145-3 when he was out in the 32nd over.
O'Brien then guided the innings through the fall of the next four wickets and into the 43rd over, matching the highest score by an Ireland batsman against India. Porterfield set the mark at 75 in 2011. O'Brien was also one run short of Misbah-ul-Haq's 76 — the highest individual score against India this tournament.
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