Smith hit 51 in Tuesday's quarter-final win against Glamorgan, coming in lower down the order at five to steady the ship after a flurry of early wickets put Durham in danger of collapse.
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However with a strong bowling attack at Durham's disposal, the Luton-born batsman was confident of progress to the semis.
"Anything over 140 we'd have definitely taken and expected our bowlers to defend that," he said.
"Obviously we were probably a few short in the end but with [Steve] Harmison, Liam [Plunkett] and Shaun Pollock bowling as well as they can it was always going to be tough for Glamorgan."