Robertson sees Spain shock as proof of Scotland's rise
Qualification for Euro 2020 ended a 23-year wait to reach a major tournament and Scotland are well on course to reach a second consecutive European Championship after taking maximum points from their opening two qualifiers.
Scott McTominay was the hero as the Manchester United midfielder scored twice, just as he did as a substitute in a 3-0 win over Cyprus on Saturday.
Clarke took charge in May 2019 after Scotland's last qualifying campaign for the Euro began with a humiliating 3-0 defeat in Kazakhstan.
The former West Brom and Kilmarnock boss was rewarded for bringing back some respectability to the Scottish national team with an extension to his contract to 2026 last week.
But even the past four years had failed to deliver a night like Hampden witnessed on Tuesday as the three-time European champions were swept aside.
"We had belief," said Liverpool left-back Robertson.
"When the gaffer took over that was what was lacking. There was a disconnect between players and fans. Let me tell you, playing in front of a full crowd makes a massive difference, but you've got to back it up with performances."
Not since Scotland beat France home and away in qualifying for Euro 2008 have the Dark Blues enjoyed victory over a major power in European football.
'Feet on the ground'
Even that campaign ended in disappointment as Scotland missed out on qualification to Les Bleus and Italy.
Clarke was characteristically calm and warned of the perils that lie ahead.
Norway and Georgia, who boast two of the world's most feared attackers in Erling Haaland and Khvicha Kvaratskhelia respectively, are next up in June.
"One bad game can set you back, so we stay focused and keep our feet on the ground," said Clarke.
"I'll have a couple of quiet days to calm down, and then we start preparing for two big games, because June could be a pivotal month for us."
But there is reason for Scotland fans to believe that there will not be crushing disappointment at the end of the qualifying campaign this time.
Spain's defeat at Hampden is part of a six-game unbeaten run in competitive games for Clarke's men, which has also secured the insurance of a playoff via the Nations League should they fail to finish in the top two of Group A.
"The gaffer's been consistent with the squads he's picked, and you can see that with the number of caps we've got now," added Robertson.
"When he took over there wasn't that experience and now we've got lads on high thirties, early forties and that makes a huge difference. When it comes to these games, you've got to dip into your experience."
Robertson, McTominay, Arsenal's Kieran Tierney, Aston Villa midfielder John McGinn and Celtic captain Callum McGregor have become almost permanent fixtures, undaunted by the challenges of international football thanks to their abundance of Premier League and Champions League appearances.
Young defenders Ryan Porteous and Aaron Hickey have also coped admirably with the step up to international level.
The problem remains further forward in the lack of a world-class striker.
But after scoring just once in his first 37 internationals, McTominay has proved to be the temporary solution by scoring four times in the last four days.
