Dropping Starc was a 'tactical decision', says Australia coach VettoriDan Vettori said it was a "tactical decision" not to field Mitchell Starc against Afghanistan. 

ADELAIDE (Reuters) - Australia s assistant coach Dan Vettori said it was a "tactical decision" not to field fast bowler Mitchell Starc in his side s narrow win over Afghanistan at the Twenty20 World Cup as the defending champions  semi-final hopes hang in the balance.

The Australians notched up a four-run victory over Afghanistan on Friday and, having failed to lift their net run rate, the host side s chances of advancing beyond the Super 12 round now rest on Sri Lanka defeating England on Saturday.

Kane Richardson was preferred in the line-up to Starc and the move did not pay dividends as the 31-year-old was hit around the Adelaide Oval with the Afghans chasing the win.

"That was a tactical decision," Vettori said of Richardson s selection. "It was more about the effectiveness of (Josh) Hazlewood and (Pat) Cummins at the top, and their ability to take the new ball and be wicket-takers.

"Therefore that pushed Starcy into a different role, and he came up against Kane Richardson and it was thought amongst the hierarchy that Kane was exceptional at the death, and so to utilise him there as opposed to Mitch."

Richardson conceded 48 runs off his four overs and only had the wicket of opener Rahmanullah Gurbaz with his third delivery to show for his efforts as Australia laboured to victory.

"In his first over, he was incredibly unlucky," Vettori said of Richardson s performance.

"He could have had two wickets and then suddenly the whole game s turned, and that first breakthrough (Gurbaz s wicket) was a big wicket for us because he played so well and had been so aggressive.

"So we reflect on that, and I think Richo himself would say that he probably missed at the back end of two overs.

"But apart from that, the majority of his spell was what we expected."