Scotland were “architects of our own downfall” in the dramatic 34-31 defeat that gave Argentina Test series victory, says captain Hamish Watson.
The Scots led 28-13 midway through the second half in Santiago del Estero but the Pumas crossed in added time through Edinburgh winger Emiliano Boffelli.
Gregor Townsend’s side had won the second encounter last weekend.
“We let them back into the game – when we were receiving, we couldn’t get out of our half,” Watson told Sky Sports.
“Our set-piece wasn’t good enough today – it’s tough when your lineout doesn’t work. We need to stick together, and build on this for the autumn.”
Head coach Townsend took positives from the performance and was proud of his players, but accepted Scotland “should have won”.
“I’m disappointed for the players because it was a chance for an historic win,” he said.
“There were chances to be more accurate with our exits in the last five minutes.
“If we hadn’t been held up over the line it is different. It’s the players that count, and you can see from their reactions how much it means to them.
“I’m proud of the effort away from home. Each game we’ve got better on this tour. It would have capped off a fantastic tour, but we didn’t win in the end, so credit goes to Argentina.”
Townsend praised debutant full-back Ollie Smith and Blair Kinghorn’s performance at fly-half.
“There was a lot to be proud of,” added the head coach. “This experience is invaluable for our players – it’s now up to them to drive themselves in pre-season to be here in the autumn. We have to be better for those games.”
Scotland face Argentina again during the autumn internationals as well Australia, Fiji and New Zealand.