Glenn Maxwell's extraordinary batting exploits may have made headlines but coach Andrew McDonald believes the all-rounder's bowling could be just as vital to Australia's hopes of winning the World Cup.

Maxwell assured Australia of a semi-final spot thanks to a stunning unbeaten double century against Afghanistan in Mumbai on Tuesday that secured a three-wicket win after his side had collapsed to 91-7 chasing a target of 292.

Earlier in the tournament, the 35-year-old scored the fastest century at any World Cup, off 40 balls, against the Netherlands.

Yet even though the off-spinner has taken only five wickets at an expensive average of 52 he boasts the best economy rate of any Australia bowler, conceding just 4.95 runs per over at this World Cup.

Australia still have one group game, against Bangladesh in Pune on Saturday, before a semi-final against South Africa -- the last team to defeat them in pool play in India before they went on a six-game winning streak -- in either Mumbai or Kolkata next week.

McDonald has no doubts about Maxwell's role in support of in-form leg-spinner Adam Zampa.

"Him (Maxwell) as the second spinner has been really pivotal in the role that he's played," McDonald told Australian on Thursday.

"We talk about him and his batting in one space, but I think his bowling has allowed us to function as a team differently to potentially how we saw it coming in and potentially how everyone else saw it coming in."

Steve Smith missed the Afghanistan game following a bout of vertigo, a condition that has troubled the star batsman several times in recent years.

"He feels pretty good today, I saw him in the corridor," McDonald said of the 34-year-old Smith, who was ruled out shortly before the toss after training on the outfield.

"I feel like it (the game) just happened at the wrong time for him not to play, whereas if it had been 24 hours later, then it might have been a different decision."

McDonald added: "He was battling with his balance on certain shots. He went through some running between the wickets as well which probably aggravated it a little bit more."

With a place in the last four guaranteed, Australia do have the option to rest key players against Bangladesh.

But that could mean they have over a week's break before the South Africa match.

"Is that ideal?" said McDonald. "It might be for some but for others you want that continuity of playing to get ready for what will be a great challenge that is South Africa."

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