In the first of two stroke-play rounds that will determine the field for the knock-out phase, Roberts carded one of the most impressive efforts of the day with a four-under 66 at Royal Lytham.
His card at The Open venue was illuminated by an eagle at the 13 while a haul of five birdies included two in the last three holes.
Roberts, who stands at 6ft 4in, is a sophomore at Colorado State University Pueblo, playing on a winning conference team this year along with fellow Scots Andrew Ni and Liam Duncan.
Earlier, the Scott brothers had signed for matching two-under 70s at St Annes Old Links, where Swede Ludvig Aberg took pride of place with a 64 that ended with an eagle.
It was a day to forget for Blairgowrie teenager Connor Graham on his return to Royal Lytham, where he’d finished second in last month’s Lytham Trophy.
He struggled to a 12-over 82, leaving him with little chance of being among the top 64 and ties progressing after 36 holes.
Graham’s next chance to land the title will also be in the north-west of England after Hillside and Southport & Ainsdale were announced by The R&A as the 2023 host venues. The tournament will then pay a first visit to Ballyliffin in County Donegal in 2024.
Prince’s in Kent will stage The 120th Women’s Amateur Championship in 2023 and Royal Birkdale, a ten-time host of The Open, the year after.
Phil Anderton, Chief Development Officer at The R&A, said: "It is fitting to have our championships hosted at some of the world's finest venues over the next two years.”
The match-play stages of the R&A Girls’ and Boys’ Amateur Championships will be played simultaneously at one venue at Carnoustie in August for the first time and the same trend will follow over the next two years.
Ganton will host match play for both championships in 2023, with Fulford and York hosting stroke play-qualifying. Alwoodley will stage match play in 2024, with Moortown and Pannal hosting qualifying.
The R&A Junior Open will be played at Kilmarnock (Barassie) in 2024 ahead of The 152nd Open at Royal Troon.