India opened the scoring in the 25th minute through Harmanpreet Singh, but then conceded three field goals to suffer a defeat in the preliminary league fixture.
"The way the match turned had something to do with our non-execution of the game-plan. After we gained the lead, we stopped playing the way we were doing earlier," said Oltmans.
"Until we scored our goal, we played fantastic hockey. After the first two minutes, we controlled the game and had a lot of good attacks. But it started going down after we took the lead," the coach added.
"Losing to a very good team is part of the game. We all know that Australia are a very good side," said Oltmans.
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"We have matched them in several matches. But in the end, it is not about matching the rivals. It is about winning. Winning is something we still need to learn," Oltmans asserted.
Oltmans said it is too early to assess the extent of the injury suffered by goalkeeper P R Sreejesh, who had to leave the field in the 13th minute of play today.
"Of course, nobody likes to be injured. There's no doubt that he's a fantastic goal-keeper, but his going off the pitch was not the turning point," he said. "We got back into the game and we got opportunities."
Oltmans feels his team's performance was below par in the third quarter when Australia claimed the lead.
"We were a bit unlucky with the last goal. From our point of view, one of the Australian player clearly touched the ball with his foot," he said.
Three Indian defenders saw Australian striker Tom Wickham move sideways in front of them, without being tackled. After moving to the goalmouth, Wickham slammed the ball into the goal.
India last defeated Australia in the Sultan Azlan Shah Cup in 2015. Last year, Australia beat India 5-1 in the league encounter and 4-0 when the team met again in the final.
As the second highest ranked team in the competition, India were expected to qualify for the final along with Australia. But that could get complex after India were held to a 2-2 draw by Great Britain in the opening fixture.
"We have four points, that's it. No more, no less," said Oltmans. "Other results are not in our hands.