"But it was still a thrill, because he's not just a gold medallist. His time over 800 metres, done in February 1962, is still a national record and would still get him a medal at the Olympics.
"He was in a class of his own, but he's an ordinary sort of guy and it's very interesting to talk to him."
To be fair, Sir Peter, 78, seemed just as nervous as his opponent, as he lost in straight games. He may have been New Zealand's Athlete of the 20th Century and therefore, arguably, our greatest ever sportsman, but, as noted by Penberthy, he was a relative novice in a game that relies on instinct.
The three-time Olympic champion also had full gallery of old friends and fans, all eager to renew or make acquaintances, so he was feeling that pressure to perform.
"Bruce is a damn good player," insists Sir Peter. "Losing to him, I didn't think was too bad at all - in fact, Bruce helped me break the ice a little bit, which was good."
Certainly, he was much better for his "tentative" first outing, subsequently combining with local player Wes Willis for victory in the doubles and then beating Russian Robert Yakolev in reverse singles to seal the win for this team.
Yakolev, 85, who speaks no English, was excited to discover who his opponent was and resolved to play even harder, but maybe too hard for his own good.
After retiring from athletics, Sir Peter left New Zealand in 1971 and now resides in Dallas, Texas. He hasn't visited here in seven years and, obviously, there is a lot of catching up to do.
"It is distracting when you're trying to focus, but I don't get this attention back in Dallas, where I'm virtually anonymous, so to come back here and be welcomed is nice," he says. "I can't turn it down."
Last week, Sir Peter took the opportunity to donate some of his personal memorabilia collection to the Te Papa national museum in Wellington, a move he hoped would show New Zealand that he still cared deeply about his homeland, despite his long absence.
"That donation gave me the opportunity to say this is where my heart is and show how much I appreciate what New Zealand did for me. "
After moving to the United States, Sir Peter studied human performance and exercise physiology, and has long been an advocate for people remaining active into their "third stage" of life.
These days, he wears a substantial knee brace and also has a heart condition that forced him to give up orienteering a few years ago.
But he is obviously happy to be back in Auckland for an event that promotes health and fitness for those in advancing years.
"This is really a lot of fun and I'm enjoying it thoroughly. I've tried to live my life actively - there are some things you can't avoid, but otherwise I'm feeling pretty good.
"I'll be 80 next year, I can still play a reasonably competitive game and I like that."
If anything, wife Miki seems even more competitive. Sir Peter admits she is very keen to medal at these Games, and wants him to be in top form and well rested for their mixed doubles event.
While Sir Peter charmingly deals with his post-match obligations, playing partner Wes Willis stands sheepishly to one side. For him, this will be a memorable week in the company of deity, but it also comes with a dirty little secret.
You see, Willis and Penberthy are regular partners, and were supposed to contest this teams event together.
"He came to me and said he'd been approached to play with Peter Snell, so bye bye, Brucey," winks Penberthy. "That's what friends do to you after 30 years.
"But it was a once-in-a-lifetime opportunity for him. This has been a great day in my life, but his great day will last a few more days."
