The Brumbies could have gone top of the Australian conference but were made to rue several missed opportunities in an error-riddled second half.
Captain Christian Lealiifano admitted the game was there to be won and said his men must improve for the final six games of the season if they want to play finals.
“The Jaguares put us under a lot of pressure today. They were very physical. We had our opportunities there but just didn’t capitalise,” he said.
“We just have to be better in our attack shape, we had some opportunities, we just weren’t in position early enough to be able to execute.
“We’ve just got to keep getting better, this is a tough competition. I’m proud of the effort but we’ll need to regroup.”
The Brumbies flew out of the blocks in Argentina but it was one of their f ormer players who set up the opening try against the run of play.
The Brumbies hit straight back with a lineout trick play as hooker Folau Faingaa went down the blindside and crossed for his seventh try of the season.
The visitors took the lead when halfback Matt Lucas, who made the most of his first start this season, hit Tom Banks on the perfect line and the fullback went through untouched to score a five-pointer.
The Jaguares drew level in controversial fashion when Matias Olando appeared to be tackled by Pete Samu but kept scampering to the line to score.
It was sent upstairs but given the green light on the half hour and the Jaguares took a 17-15 lead into the break.
It was an arm wrestle in the second 40 minutes and the Jaguares extended their lead with a 61st-minute penalty.
Jaguares flanker Marcos Kremer was yellow carded for a professional foul in the 65th minute but the Brumbies couldn’t make the most of the man advantage and turn pressure into points.
It was a frustrating finish for the Brumbies as several errors robbed them any chance of victory, but the home side also appeared to simply want the win more.
2019 Rugby World Cup city guide – Osaka:
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