Thomas went into the July race in support of Chris Froome but ended up at a new level as he was pulled along in the slipstream of the eventual winner.
In many ways 2015 was a breakthrough year for the Welsh rider, with victories at the Volta ao Algarve, E3 Harelbeke, third overall at the Tour de Suisse and a fifth at Paris-Nice all early pointers to what was initially viewed as an unexpected Tour performance.
While the true nature of his talent was on display so was the grit necessary for a potential Tour winner after he rebounded from a terrifying looking crash on Stage 16 that would have shaken lesser riders.
Terrible looking crash for Sky's Geraint Thomas #sbstdf http://t.co/74AtL0CjgT — CyclingCentral (@CyclingCentral) July 20, 2015
There Thomas was forced off the road while descending Col de Manse and hit a pole before dropping down into a ditch. At the time he was among an elite group of contenders, including team-mate Froome.
He quickly remounted after the crash and recovered to finish just 38 seconds back while maintaining his sixth place in the general classification.
He ran out of gas on Stage 19 while ascending the Col de la Croix de Fer, finishing 22min behind the winner and dropping to 15th overall - his final position in Paris.
With hindsight it should have been recognised that Thomas was capable of a high Tour placing and now he believes that goal can be achieved.
“Yeah. I certainly think it’s a lot more achievable than I did three months ago. If I keep on improving, commit to it totally, have a team around me, a podium is certainly realistic," Thomas told The Guardian.
"And you’d aim to win it. You would be there or thereabouts – especially if the route was good for me. It’s certainly exciting.”
“I thought I might be up there at the thick end for a day or so. But to be there for so long was awesome. From day one I was never worrying about myself. I was always thinking about Froomey. So it definitely gave me the confidence that if I focus on it 100 per cent as a back-up GC rider, behind Froomey, and be protected myself, I’ll have a real good goal for next year.”
Sky has strenghtened its support for Froome and overall general classification potential during the transfer season, adding riders like Benat Intxausti, Michal Kwiatkowski and Mikel Landa.
And with Froome now well established as team leader and unlikely to move, will there be a place for the 29-year-old?
“I think you can have both, but it will depend on the buildup," he said. "We’re both honest enough to know that if the other guy is better we’d commit to each other. I certainly would and I’m pretty sure Chris would do as well. But it’s a tough one. It’s like the last Olympics and in the sprint you had (Chris) Hoy and (Jason) Kenny chasing one spot.”
But Thomas is clearly thinking about future possibilities should he continue to build on his Tour performance, with Grand Tour team leadership of his own one possibility.
"My deal with Sky expires next year but at the moment I don’t want to leave for another team and be their leader because Sky is the best place to learn – and be in the best position to get a result.
"Maybe two years down the line I will feel: ‘I know exactly what I’m doing now, and exactly what it takes.’ If I have to leave then, then I would.”
