A six-times winner on the European Tour where he was known for his brilliant bunker play and dogged approach to the game, Johnstone will be one of three assistants to fellow Zimbabwean Price in the 10th edition of the biennial team competition.
The Internationals will be striving to improve a dismal record of just one win against the United States since the Cup was launched in 1994 and with Price identifying team spirit and fun as crucial to achieve success, Johnstone is a perfect fit.
"Tony is going to be such an asset to the team," Price, who has known Johnstone since they played junior golf together, told Reuters ahead of the Oct. 3-6 Presidents Cup at Muirfield Village Golf Club.
"Ever since I selected him as one of my co-captains, he has been so excited about this. He has phoned me like three times a week. He is just so into it and I love it.
"He's looking at all these stats, and scratching his head and trying to figure out who will be best playing with who. The camaraderie and the energy and the fun that Tony will bring to the team will be fantastic for us."
The two most experienced players on the International roster, Masters champion Adam Scott of Australia and four-times major winner Ernie Els of South Africa, were both delighted to hear of Johnstone's appointment as an assistant.
"Adam was so happy when I first went to him," Price grinned. "He said to me, 'Please tell me that you have got Ovies as an assistant captain.' And I said to him, 'Absolutely'. And Adam just started laughing."
The charismatic Johnstone, a fiery and fidgety player who relishes practical jokes and speaking his mind, has had the nickname 'Ovies' since his days in junior golf where he was often reputed to want a "do-over" out on the course.
Els, who will be competing in his eighth Presidents Cup next week, also knows the 57-year-old Johnstone very well, having competed against him regularly on the Sunshine Tour in South Africa and also in Europe since the early 1990s.
"He's going to be great," Els told Reuters. "The guys that don't know him that well, hopefully they will get to know him quickly because he is very funny and very uplifting. He's got a lot of fight in him, and that's the way he played the game."
Johnstone was diagnosed with Multiple Sclerosis in 2003 and told he would never play golf again but, helped by his fighting spirit and a revolutionary drug treatment, he returned to the game and won his first over-50 title at the 2008 Jersey Seniors Classic, a triumph he described as the proudest of his career.
He now splits his time between competing on the European Senior Tour and working as a golf analyst on television.
Price selected fellow Zimbabweans Johnstone and Mark McNulty, along with Japan's Shigeki Maruyama, as his assistants for the Presidents Cup and has been clear-cut about their role.
"The American team is going to be a lot stronger on paper than our team but the camaraderie, willpower and spirit of a team can overcome a lot of things, so that's one of my prime objectives," Price, a three-times major winner, said.
"It's going to be up to me and my assistant captains to really get the players fired up. They'll have me, Mark, Tony and Shigeki as their skivvies ... so I have told the players to make the most of it. But we'll have a lot of laughs."
Price will have a fourth Zimbabwean to rely on next week at Muirfield Village with his compatriot Brendon de Jonge set to make his debut for the Internationals in the team competition.
De Jonge will become the third Zimbabwean to compete in the Ryder Cup-style event, following Price (1994, 1996, 1998, 2000, 2003) and Mark McNulty (1994, 1996), and is already looking forward to the influence of Johnstone in the team room.
"Tony's about as funny as it gets," de Jonge told Reuters with a quiet chuckle. "I've heard quite a few stories about him that I probably shouldn't repeat.
"He is going to make it very, very relaxed and very, very enjoyable for the Internationals. He will be invaluable."
Having played most of his professional career in Southern Africa and Europe, where he won the Tour's flagship PGA Championship in 1992, Johnstone is not well known in the United States.
However, his reputation for being wildly funny and often self-deprecating is growing rapidly on Twitter where he regularly posts an array of humourous quips and hilarious pictures.
Talking about South Africa's legendary putting supremo Bobby Locke, Johnstone tweeted: "Locke could hole putts on a hedgehog's back. Would start tipping his cap when the ball was 10 feet out!"
In another recent posting, he said: "Scariest thing about Friday 13th?? Its official name is "Friggatriskaidekaphobia". Gawd. No wonder I'm locked in the cupboard!"
On and off the course, Johnstone has always been irrepressible. Expect more of the same at Muirfield Village.