New Zealander It's A Dundeel underlined his star staying qualities with a rousing Group One Spring Champion Stakes victory over the previously unbeaten Proisir.

Proisir had been emphatic in his three wins leading into Saturday's Randwick feature and was sent out a dominant $1.28 favourite.

It's A Dundeel, trained by Murray Baker, also went into the race unbeaten and was the only other horse given a chance at $6.50.

The two colts didn't disappoint, clearing out in the straight and settling down to fight the race out.

Proisir sprinted better than his Kiwi rival to pinch a break but It's A Dundeel's stamina shone through and he knuckled down to his task, reeling Proisir in to post a thrilling short neck victory.

Honorius ($21) was five lengths away third.

"It was a great race, two great colts fighting it out like that," Baker said.

"He's only small. I've got a half-sister to him at home and she's bigger than him and she's only a yearling.

"He's got a big motor. He knows how to hit the line. He can really run that last 100 metres."

It's A Dundeel will head to Melbourne for the Victoria Derby (2500m) and while he is still in the Cox Plate mix, Baker says he is unlikely to head to the weight-for-age championship.

James McDonald rode the winner and had no doubts he would run the Derby trip.

"He silenced a few critics today. He's under-rated," McDonald said.

"He's going the right way into the Derby. He has a great will to win.

"He will get the 2500 metres."

Rawiller wasn't disappointed in Proisir.

He viewed stewards' footage of the finish to see if there were any grounds for a protest as It's A Dundeel was green in the straight.

But correct weight was declared.

"I thought he (Proisir) was brilliant. Not much went our way," Rawiller said.

He also paid tribute to It's A Dundeel.

"He's an exceptional stayer. It took one to beat us to be honest."