The Dumfries & County player birdied his last two holes at Kingswood Golf Estate in George for a four-under-par 66, setting the pace along with Frenchman Edgar Catherine and South African Phillip Swanepoel.
Johnson said competing on similar greens during a four-year stint at Chattanooga University in Tennessee helped him to come to grips with the grain.
“I haven’t played on greens like these in two years, but having played them certainly helped,” said the 24-year-old.
“The weather was good with just a breeze, so you had to take advantage. I short-sided myself at one par five and one par four, so I’m very pleased with the start.
“My only bogey was a three-putt at 14, but this was my first competitive outing since November last year, so I’ll take a 66 to the bank.”
Johnston, who reached the second stage in last year’s European Tour Qualifying School, is bidding to add to South African Amateur Championship successes recorded by Michael Stewart, Brian Soutar, Daniel Young and Craig Ross on similar trips by Scottish Golf squads in recent years.
Kirkhill’s Ross, who defends his title later this month, is sitting joint-18th after a 68, one ahead of Craig Howie (Peebles) and Jamie Stewart (Old Ranfurly). Cawder’s Calum Fyfe and Eric McIntosh (Bruntsfield) had 75s while Sam Locke (Banchory) signed for a 77.
Two other Scottish amateurs, Barry Hume and Euan McIntosh, will be hoping to make their presence felt in the Portuguese Amateur Championship, which gets underway today at Montado Golf Resort.
It’s a first outing for Hume since the Haggs Castle man was named in the Great Britain & Ireland squad ahead of this year’s Walker Cup in California while McIntosh from Turnhouse will be looking to produce the form that saw him top the Scottish Order of Merit last year.
Danny Willett is hoping to kick-start his 2017 European Tour season at this week’s Maybank Championship in Malaysia.
The reigning Masters champion began the season with a top-10 finish at the UBS Hong Kong Open at the end of last year, but has not quite continued that form into 2017.
The Englishman will play his first competitive round at Saujana Golf & Country Club, and he is feeling confident having performed strongly in Malaysia in the past.
“This year has been a little bit slow so far but hopefully we can keep progressing,” he said.
The event sees another Augusta winner, Charl Schwartzel, make his first appearance of the year.
“I struggled with my knee a little at the end of the year and it never really got better so by the time it came to January for my MRI scan it turned out I needed a longer break,” said the South African.
“That has actually allowed me to be a lot fresher than I think I would have been, to sort out some of my clubs and get some practice done to get my game in shape.
“I think overall it’s been a good thing. It’s been nine weeks since I last played competitively and it’s the freshest I’ve ever been.”
For the second week in a row, Marc Warren and Richie Ramsay are set for early starts in the opening round.
Warren is out in the third match with Edoardo Molinari and Arjun Atwal, with Ramsay just behind him in the company of Jeev Milka Singh and Hennie Otto
David Drysdale, the only other Scot in the field, is out in the afternoon wave with Gregory Bourdy and Sukree Othman.
Five Scots, plus Edinburgh-based Beth Allen, are playing in the LET’s opening event of 2017 - the Oates Vic Open starting tomorrow in Australia.
The event, which is being held at 13th Beach Golf Links in Barwon Heads near Melbourne, is one of three new tournaments that have been added to the schedule this year.
And, for the first time in history, LET players will compete for equal prize-money with the men, as both the men’s and women’s Oates Vic Open fields will be playing for identical purses of £305,000.
Aiming to get their seasons off to flying starts by securing a chunk of that are Kelsey Macdonald, Michele Thomson, Carly Booth, Gemma Dryburgh and Kylie Henry.
The latter will be aiming to take up where she left off when finishing strongly to claim a share of sixth spot in last week’s RACV Gold Coast Challenge.
For Allen, the event marks the start of her defence of the LET Order of Merit title, having become the first American to claim that prize last season.
Allan Patterson, estates and courses manager at Trump Turnberry, will be among the speakers at the upcoming BIGGA Scotland Golf Industry Conference.
Taking place at Perth Concert Hall on 7 March, the conference is the flagship event of the 2017 calendar for the British & International Golf Greenkeepers Association’s Scottish Region and brings together professionals from around the country and from all sectors of the golf industry.
Also speaking at the Scottish conference will be Dr Steve Otto, director of research and testing at The R&A, and course designer Martin Ebert, of MacKenzie and Ebert.
“I am really looking forward to hosting the conference and I believe the line-up of presenters we have is exceptional and sure to appeal to many,” said BIGGA Scotland chairman Stuart Ferguson.
“The conference will conclude with a presentation from Allan Patterson on the redesign of Trump Turnberry, and I know fellow greenkeepers will be excited to hear what he has to say.”
The recently-launched World Masters Golf Championship has received a significant boost with the announcement that The Scotch Malt Whisky Society will be a partner for the championship in its inaugural year.
The event is open to all golfers with an official handicap who are over 50 years of age as at 17 September, 2017.
It will be stagedfrom 18 to 21 September 2017, on some of the country’s top courses, including Prestwick, Dundonald, Western Gailes and Royal Troon.
Spanish duo Sixto Casabona and Carlos Garcia Simarro are out in front heading into the final round of the PGAs of Europe Fourball Championship at Lumine Golf in Tarragona.
Following opening rounds of 66 and 63 for a 14-under-total, they hold a one-shot advantage over Liam Murray and Xavier Puig.
Javier and Manuel Ballesteros, the first-round leaders following a 64, slipped to jointp-15th after a second-round 72.