Paul Grayson top-scored for the visitors with 59 in their modest total of 194 but Durham lost seven wickets for 25 runs late in the day and Pratt, making his Sunday League debut, came in at 188 for 9 with three balls left.
He turned Ronnie Irani to fine leg for three, Mike Foster scored a single and off the last ball Pratt took two to extra cover.
Brian Lara could only watch from the pavilion, suffering a bruised leg, as his Warwickshire team romped to the top after a 47-run win over Derbyshire. Lara was injured when he pulled a ball from Dominic Cork into his leg.
Chris Adams celebrated his England call-up with 100, hitting three fours and three sixes, as Sussex recorded a 28-run win over Nottinghamshire at Trent Bridge.
Courtney Walsh took 5 for 2 with his last 14 deliveries to help Gloucestershire to a four-wicket victory over Leicestershire at Bristol.Reuse content