The Saints are working hard to prepare for the new Premier League season, which begins in the middle of August.
"I think it was a serious performance today," Hasenhuttl told BBC Radio Solent.
"You never know against a Championship team. In the beginning you have to fight to come in the game.
"In the first half you could see it was not so flowing.
"After the first goal you could see it was a little bit better.
"It took a while until we had the first chances, but you have to be patient to get chances.
"Because you know against a good defending-deep team in the beginning, it always takes a little bit of time. This is normal.
"But I think the longer the game went on, the more chances we had."
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