Campbell also said it was "weird" playing in front of no crowds, in what was the European Tour's first event since the sporting shutdown caused by the coronavirus pandemic.
"My expectations were pretty much none. I wanted to get out here and enjoy myself. It's weird with no crowds, no clapping. I think I made six birdies today and nothing there. It's kind of weird, it's like playing with your mates – more intense, but it's the first time for me not playing in front of a crowd. It's very different indeed.
"I've had a good career the last 20 years, winning 15 times around the world, that's good enough for me. If I have another one this week it's a bonus."
Campbell, who fell off the golfing radar after struggles with injuries and form, said his first round score was his best in at least a decade on the European Tour.
He may have gotten some inspiration from his 21-year-old son Thomas who is caddying for him at the tournament.
"It's like having 15 clubs in the bag," Campbell said. "The thing is, unfortunately when I had my success from 1999 to 2005 he was so young, he can't remember. For me it's having fun with my boy, bonding with him. He gave playing up a long time ago, he was a good player but didn't like the attention."
Regardless of how he goes in the rest of the event, Campbell says he intends to continue his storied career by playing senior golf in the United States. However, he admitted it hasn't been easy qualifying for the Champions Tour.
"It's my intention to play senior golf. I feel like I'm competing more there," he said. "My main focus is on the Champions Tour but it's hard to get in there. I asked for 15 invites last year and got one. It doesn't mean much, being a major winner."
Fellow Kiwi Ryan Fox is in a tie for ninth after carding a 67.
Law of Scotland shot a seven-under 64 to take a one-stroke lead over Oliver Fisher, Garrick Porteous and Renato Paratore into the second day.