Portugal played ball in hand and even led 7-3 early on after Pedro Bettencourt's try, although they could not eventually keep up with the two-time world champions' physicality, losing 34-14.
"This team has things to improve and work on but we have a lot of pride having challenged this Australian team," Lagisquet, who led Biarritz to the French title three times as a coach, told a press conference.
"But there is also disappointment because with more experience we might have had a different goal. We played total rugby and total rugby is very exciting for a coach and the players."
Playing was not enough, however, as Australia's power proved too much to handle, with Eddie Jones's side making the most of Bettencourt's yellow card to score three tries in the space of seven minutes.
"I was concerned about the physical power of the Australians and most of their tries came from that physical impact," former France winger Lagisquet, who scored four tries in the World Cup, said.
"There were a lot of missed tackles. We needed to adapt ourselves to the circumstances but we couldn't."
Next up for Portugal, who were only beaten 28-8 by Wales and drew against Georgia, is Fiji, who might rest key players as they only need a point to qualify for the quarter-finals.
"We want to compete against Fiji. It's our last chance to prove ourselves so we're going to go all in," captain Tomas Appleton said.
"We're not fully professional and we have made a lot of sacrifices. But when we beat the U.S. to get to the World Cup, we said we're going to compete against every team, it doesn't matter who they are, we're going to compete."
Australia, certainly, were impressed, and man of the match Rob Valetini predicted a bright future for Portugal.
"Credit to Portugal, they are a very solid team. I can't believe this is their first World Cup (since 2007). I know they are going to be a powerhouse in a couple of years," he said.
