"It sort of happened in a blur because it sort of came over and I was like, 'I have a chance here' and then I just put [my hand] down the wall," he said.
"I'm not left handed but somehow I put it there and it stuck. Then everyone was just jumping all over me ... I actually just caught it and I was like, 'Holy!'
"It just went really quickly and I didn't really catch onto it until now. It still hasn't sunk in really it's all a bit of a blur."
Martin Guptill (105), the top-scorer in New Zealand's innings of 243-6, also paid tribute to Grimstone's effort in a post-innings interview.
Guptill smashed nine sixes on route to his second T20 hundred.
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