World No.7 de Minaur cut a subdued figure in a sub-par 6-3 6-3 defeat to Ruud during Australia's opening United Cup victory against Norway in Sydney on Saturday.
It was de Minaur's first defeat to Norway's world No.12 in three ATP matches dating back to 2019.
The 26-year-old, who will lead the local charge at Melbourne Park alongside rising talent Maya Joint, admits he made uncharacteristic mistakes against the three-time grand slam finalist.
De Minaur delivered eight double faults on his home court as he struggled to flaunt his second-serve prowess against a "super aggressive" Ruud.
Last season on the ATP Tour, de Minaur was second only to world No.2 Jannik Sinner for the the highest percentage of points won on second serves, but he was well down on his average on Saturday.
"It's not really part of my DNA to throw in so many faults," de Minaur said.
"Today, more than anything, it was just getting used to the conditions.
"I struggled a little bit, playing at night a little bit heavier.
"I felt like I wasn't able to get that feeling on my serve of kicking in, which in the past I've had no problem doing.
"I lost a little bit of rhythm, more than anything, and Casper came out playing super aggressive."
But de Minaur said he hadn't felt mentally oppressed by Ruud, despite conceding the opening three games in less than 12 minutes.
"I was in a good mindset, and even after the match, I'm able to process this match correctly," de Minaur said.
"There are a couple of things that I can do better, but also understanding that it is the first match of the year.Â
"Ultimately, season's back on, so hopefully, I can flip that switch and more than anything, execute in those important moments."
After defeating Malene Helgo in the women's singles as a last-minute replacement for Joint, popular veteran Storm Hunter linked up with John-Patrick Smith in the mixed doubles to snare a 2-1 win over Norway.
De Minaur will look to return to form on Tuesday for Australia's tie against the Czech Republic, slated to face world No.19 Jakub Mensik.
Australia will also hope Joint will recover in time to face two-time grand slam winner Barbora Krejcikova after being ruled out of their Norway tie with illness.
"Look, at the end of the day, it's not life or death," de Minaur said.
"I've had numerous times when I've lost the first match of the year, and then come out and have found my tennis straight away."
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