Sabella's team were nowhere near their best in Bucharest on Wednesday, with captain Lionel Messi particularly underwhelming as he appeared to struggle with illness.
Sergio Aguero's lively performance provided the only real bright spark for Argentina, but Sabella remained defiant after his side's final friendly before he names his FIFA World Cup squad, suggesting that his players were merely a "little tired".
"This was a game we thought we were going to win and I think overall, we deserved to win," he said.
"Most of the players that played tonight played on Sunday. The flights for some of them were a bit long. They arrived a little tired and had only one day of training.
"Obviously, when we have more time to rest we will be better."
Sabella went on to dismiss any notion that Messi, who vomited on the pitch shortly after kick-off, was primarily to blame for Argentina's lack of cutting edge.
"I think Messi had a good game with major sparks. It just happens that the Romanian team was grouped well back," he added.
"I would say the first half cost us. There were more sparks than creative plays. But during the second half we played more as a collective than one with individual sparks."
