''I imagine I will be [nervous] over this one,'' Williamson said.
''He's an outsider so there's not much pressure but there'll be a few jitterbugs.
''Probably round at the start I'll start feeling it a little bit - that will be the most nervous time - or going out there for preliminaries when you're not 100% focused.''
Williamson has been close to a drive in New Zealand's biggest harness race on the calendar in the past, just missing out on taking the reins behind Lord Forbes (2010) and Rangataua Ray (2012).
He is in his first year as a senior driver, and has leading driver Dexter Dunn to thank for his New Zealand Cup engagement.
''They asked me to drive it the very first run it had this time up,'' Williamson said.
''Dexter was away on holiday and [Four Starzzz Flash] ran third. I looked after him and he ran home really good.''
Four Starzzz Flash booked his place in the New Zealand Cup with a win in the Maurice Holmes Vase in early September.
Dunn was always going to stick with Christen Me for his New Zealand Cup drive, which meant Williamson got the call-up to steer the 7yr-old son of Four Starzzz Shark today. So, when Williamson takes Four Starzzz Flash on to the track shortly after 5pm, he will be able to tick a major achievement off his list.
''It's always been the one thing I've wanted to have, so it's awesome to get it this early,'' he said. The Cran Dalgety-trained pacer has form over 3200m, having won the Ashburton Cup in 3.59.5 last year. Williamson is aiming for a top-five finish.
''The first three or four runs this year proved he could compete with them if he got a trip [a good run in the race].
''If they go hard and he was back on the rail in the right mood, top five wouldn't be beyond him.''
And if the unthinkable happens and Williamson returns to the winner's circle at the head of the field?
''That would be just awesome. I imagine if he won it, it would lead to a very bad headache the next day and some silly celebrations.''
