Steve Smith said Sunday he felt obligated to step up and replace David Warner as Australia's Test opener, but also admitted it suited him because he got bored waiting to come in at four.

The 34-year-old veteran was a surprise pick to do the job ahead of openers Cameron Bancroft, Marcus Harris and Matt Renshaw after Warner bowed out of Test cricket this month.

He will pad up in his new role for the first time in the opening Test of a two-match series against the West Indies in Adelaide, which starts on Wednesday.

"They (selectors) were obviously very keen to get Cameron (Green) in the side as well and play our best six batters, and for me it didn't sit right to have him come in and bat up top," he told reporters.

"I've played for a long time and I'm an experienced player, and I think it's something I should have done."

The highly rated Green has been sidelined recently by a resurgent Mitchell Marsh, who has assumed the all-rounder role.

Shifting Smith up the order, rather than opting for a specialist opener, allowed selectors to bring Green back primarily as a batsman.

Smith revealed he had been mulling the idea as far back as the Ashes in England last year, but the prospect only crystallised during the third Test against Pakistan in Sydney this month.

"I'm looking forward to the opportunity of getting in and facing the new ball," he said.

"It's something that isn't really foreign to me. I've batted on numerous occasions where I've come in early doors and I batted at number three for quite a while."

Former skipper Smith, who has played 105 Tests and accumulated 9,514 runs, also admitted that coming in early suited him because "I don't like waiting to bat".

"I actually don't like watching cricket that much, believe it or not," he said.

"I'd prefer to be out there batting. It gets a bit boring sitting there (with the pads on) but I don't have to do that any more."