The spelling paddock worked against his horse and there's a formidable weight-for-age rival waiting for him but Chris Waller is adamant Boban is on target for the Expressway Stakes.

Already one of the best-backed runners at Randwick on Saturday, Boban will be attempting to stretch his winning sequence to six races in the Group Two sprint.

But the four-year-old, mentioned as a serious chance for 2013-2014 Australian horse-of-the-year honours, must overcome an ineffective spring break - and Rain Affair - to keep the streak going.

"I thought he spelled poorly," Waller said.

"He's just that type of horse that he is better in the stable and as the preparation goes on he just seems to strengthen up and really thrive."

Boban rushed through the classes during a spring campaign which netted Group One wins in the Epsom Handicap and Emirates Stakes to stake an early claim for Australia's horse-of-the-year award.

But he will be stepping out in weight-for-age company for the first time in the Expressway with one of Sydney's fastest horses, the Joe Pride-trained Rain Affair, ready to rumble.

"If Rain Affair is at his best he would win ... you couldn't beat him over 1200 metres," Waller said.

"It will be a genuinely run race and that will help Boban so it will be an interesting race."

With Nash Rawiller warming the saddle for suspended Glyn Schofield, Boban has been backed from $3 to a clear-cut $2.50 to pick up from where he left off in the spring.

But Pride says Rain Affair will have an uncontested lead, a key factor in the sprinter's chances.

"On paper it's just nice to see that nothing will be up there possibly attacking him," the Warwick Farm trainer said.

Waller will also run Queensland Group One winner Sizzling and middle-distance galloper Moriarty in the Expressway.

They are not expected to figure but Waller says it won't be long before stable newcomer Sizzling shows his class.

"He's done very well but to me he looks a second-up horse," Waller said.

"Second-up he will be where we want him to be and that will either be in the Apollo Stakes or the Futurity Stakes in Melbourne."