It was a huge day for the Crawley club and the biggest game in their history. And at the halfway stage Joe Walker would have been happy with his team's total as they posted 237-3 from their 40 overs.
O'Donnell finished on 105 not out while Walker hit 47. There were good contributions from Conor Golding and Danny Alderman.
But the Essex side ended up victors in a thrilling game, winning by five wickets with two balls to spare.