Australia made fewer tackles than Fiji and were successful 65 per cent of the time versus 77 percent for Fiji.
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The biggest blight on Australia's copybook was its penalties conceded. In total, they racked up 18 while Fiji conceded just seven.
That proved to be the difference in the end. Australia scored two tries to one, but Fiji slotted five penalties.
While Horwill said the 28-8 win for Wales over Portugal "wasn't overly impressive", he's conscious there are holes in the Wallabies that can be exploited in their forthcoming encounter.
"It's a big challenge for us against them next weekend," said Horwill on Stan Sport's Rugby World Cup Central.
"It's a pool-deciding match for the Wallabies and it's a huge challenge.
"It'll be a much different challenge to what the Wallabies have faced against Fiji. Less of that sort of broken field, big, dominant ball-carrying.
"They're going to play a much more tactical game, squeeze, a lot more kicking, tactical kicking, pressure.
"The breakdown will be so important. It's something that we lacked against Fiji was our breakdown accuracy.
"I think that's where Wales would have watched our game and gone 'That's where we need to attack' and Warren Gatland will be working his team to do the same."
Like Horwill, fellow ex-international Tim Horan bemoaned the penalty count that gifted Fiji easy points.
With a few issues to worry about, Horan wonders if there'll be sweeping changes to turn the tide against Wales.
"Once again, penalties. I think it was 17 or 18 penalties in the game. Only seven penalties against Georgia last week – that's because they didn't have as much pressure coming through from (Georgia) as they did here (from, Fiji) today," Horan explained.
"When you look at Eddie Jones, what does he do with his team? Does he stay and stick with the players he's got there? There were a lot of changes made in that second half.
"I thought Ben Donaldson, when he (moved to fly-half) in the second half, got a bit more width in their game. Big challenge now for Eddie Jones. Of course, this is a massive game in seven day's time against Wales.
"You've got to beat Wales to make a quarter-final. Eddie Jones and the team, they'll have to regroup, they'll get back on the horse and find a way to get to the breakdown, be more active there, and also their carries. They didn't bend that defensive line."
Australia will face Wales on September 25 at 5am.