Thomas lost his chances of winning the Tirreno-Adriatico overall, one year after doing so in Paris-Nice, when Team Sky suffered from three wheel problems in the opening team time trial, losing more than a minute to the other overall contenders.
However the Welshman drew inspiration from Barcelona's overturning of a 4-0 first leg deficit in the Champions League to win 6-5 on aggregate against Paris St Germain as he took a fine solo victory.
"It was a massive disappointment yesterday," Thomas said of the team time trial. "We came here to win the GC, with myself and Landa with a two-pronged attack, so that was massively disappointing for how it ended yesterday.
"We saw the Barcelona result last night and that shows anything can happen in sport. We wanted to be aggressive and race every day as best. I had my chance today and I was lucky to finish it off."
Thomas attacked in the undulating Tuscan hills. He first marked Bob Jungels (Quick-Step Floors) then attacked, at 4.8 kilometres remaining, to pull away Jungels, overall leader Damiano Caruso (BMC Racing) and Jonathan Castroviejo (Movistar). Not happy with his companions, he surged free with 3.9 kilometres remaining, maintaining his advantage on the final kilometre kick into Pomarance.
It was his first win since the Paris-Nice overall last March and his first win in Italy in an 11-year professional career. He gained time bonus and a handful of seconds on the favourites, like Nairo Quintana (Movistar) and Thibaut Pinot (FDJ), but not enough to think of the overall classification when the race ends Tuesday along Italy's east coast.
"Barcelona start from scratch in the quarter finals, we don't. But never say never," Thomas said. "The thing is to try to keep race aggressively every day and try to take wins.
"We have Elia Viviani for the sprint tomorrow and other guys for the mountain top finish. I'm not thinking of the GC now but if something happens, fantastic. But I'm just treating it as a good chance to race for stages."
Thomas could ride clear on the 16.1-kilometre climb to Monte Terminillo, where Quintana won in a snow storm two years ago. If he gained enough time, he could perhaps re-join the overall classification hunt.
Chris Froome is watching closely. Thomas helped him win the Tour de France three times and decided to switch focus to winning the Giro d'Italia this May before going to the Tour.
The two trained together for two weeks at altitude in South Africa last month. It was the first time that Thomas spent such a long time alone with is long-time team-mate and cycling's grand tour star.
"I've raced in all three of his wins, you learn the most there when the pressure is on," Thomas said. “Then training with him in the last month too, it pushes you every day, you are always testing yourself against him, there's no other better training partner.”
Yesterday, Froome sent Thomas a message after seeing the team's disastrous time trial. Gianni Moscon hit a hole in the road and his carbon front wheel collapse in pieces. The team was forced to wait as it lost others to wheel problems as well.
They did not speak about the parliament and UKAD investigation into Team Sky and British Cycling.
"I haven't spoken to Froomey actually. Yesterday, it was about what happened in the stage, saying sorry and things. I haven't spoken with him about that [the Team Sky situation]."
He explained that it was the same with Dave Brailsford, the team's founder and boss. Yesterday, Brailsford arrived in central Italy to watch Landa and Thomas race together.
"He showed up just before the team time trial and he shook my hand and said thanks for yesterday [for the Twitter support]. That was it, we didn't speak but focused on the race. After race, there was a lot of other stuff going with wheels and stuff."
There had been reports that Brailsford may be forced to step down. Then on Tuesday, Sky and Brailsford issued a response to UKAD's comments and the parliament's inquiry. Thomas saw the document, but said that he is in "a bubble" and is "trying to lose weight and get fit."
"The riders speak to each other, but it's more about... It's nothing to do with us. It is indirectly because we are in Team Sky, but it's more an issue for the management and the medical team," he explained.
"They put this document together but we didn't see it until it came out. I haven't read it all. Six pages is quite a lot to read. I've just got confidence in the team and that's that."
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