The Wallabies claimed the Cook Cup with a 20-14 victory at Twickenham.
"We were not clinical enough," Robshaw told Sky Sports 1.
"All credit goes to them. They came here and did a job. We need to go away and look at where we lost points."
England choose to run the ball rather than go for three points in the second half, for which they failed to add to their points tally.
"You need to make sure if you do go, you come away with the points," Robshaw admitted.
And asked if the best team won, he said: "Potentially."
Australia captain Nathan Sharpe said: "We spoke about character and resolve this week and I thought the effort was outstanding."
Australia's scrum had been put under the microscope in the lead-up to the match and Sharpe added: "Our scrum was outstanding."
England coach Stuart Lancaster said his side did not underestimate the Australian scrum.
"Disappointed with the scrum, particularly with the penalty count," he said.
"But overall we have to make sure we manage it on the day."
Lancaster said he was disappointed with the result.
"We put alot of pressure on them and we didn't come away with points when we needed to," he said.
"We have got to take those points when we are in the red zone."
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