The ability to withstand pressure has taken Jim Cassidy a long way in his career, but he admits he felt it more than usual leading up to his 100th Group One win.

Not because the number was so important to him, but because the Coolmore Stud Stakes at Flemington was vital to Zoustar.

Widden Stud secured the colt for a reported $16 million this week with $4 million bonuses and the colt's future career on the line on Saturday.

"I reckon I've had more pressure on me today than any other Group One I've ever ridden in," Cassidy said.

"His balls were on the line and so were mine."

"What with the sale of the horse and the boom me and Chris (Waller) have put on him, it's a relief.

"You can say anything, but you have to stand up and be counted."

Cassidy said he was frustrated by the slow early pace in the Coolmore (1200m), but knew he had the horse underneath him.

"They weren't going fast," he said.

"To expose one like that for 1200 metres was hard. I had nothing to cart me into the race and I was just swinging off him."

The Waller stable has given Cassidy his past three Group One winners, two with Zoustar and the Queensland Derby with his Melbourne Cup ride Hawkspur.

The first Tuesday in November marks the 30th anniversary of Cassidy's first Melbourne Cup, when the then 20-year-old raw New Zealander steered Kiwi to a memorable win.

The jockey's career has reached dizzying heights and, at times, the lowest of lows including a ban in the wake of the infamous "jockey tapes" scandal of the 1990s and serious injuries along the way.

But Cassidy prefers not to look back or forward and retirement is not on the radar.

"I live day to day, year to year," Cassidy said.

"This is my job. My priority is my family, my wife and kids.

"I don't think about retirement, especially not when I've got Zoustar and Hawkspur. I'm not going to let anyone else get on them.

"While I've got the carnival rides I'll keep going.

"I'm not going to punch slow horses around Canterbury midweek.

"I've worked my way up to get here.

"I've been at the top for 30 years and today goes to show I still am."