Sky lost 47 seconds in the team time trial to stage winners Mitchelton-Scott with leader Adam Yates, 40 to Jumbo-Visma with Primož Roglič and a little less to others including Tom Dumoulin (Sunweb).
"It's not ideal, certainly, but you never know with bike racing," Thomas said warming down on his trainer.
"They did a real good strong ride, and unfortunately we are quite far behind, but it's still six days of racing to go."
After the early morning showers cleared, they completed the 21.5km stage in 23-12 minutes and averaged 55.603kph, placing fifth.
The 2018 Tour de France winner did not know about the time Yates had set, but already showed concern for Roglič's gains.
"We saw in UAE he's going well and he's going for the Giro so obviously he's in good shape now and he's got a strong team around him," Thomas said.
"For sure he's the favourite but like I said we'll see what we can do."
"Our ride? Good actually, we did it really good," Dumoulin explained.
Sunweb rode to third place, losing only 22 seconds to Yates and 15 to Roglič.
"We had a completely different team than in the UAE Tour. A couple of guys the same and others different, it's always tricky, we made a couple of small mistakes."
The 2019 Tirreno-Adriatico lacks any summit finishes for the first time in years. The tricky medium mountain stages through the Apennine Mountains and in regions like Marche will force the stars on the attack in unlikely places.
Adam Yates celebrated near the podium with his team, but not too much with the week ahead. "It'll be tough," he said. "There's no real big super hard mountain stage, there's a lot of punchy stages."
"If I'm in good shape I like to race," Dumoulin continued. "Definitely, I'm here to at least try to win Tirreno so we'll see how it goes."
Thomas last year was in position to win the race overall until he had a chain problem on the summit finish climb. His team-mate Michał Kwiatkowski instead won the 2018 edition. This week, Kwiatkowski is leading the Paris-Nice stage race with Egan Bernal as a second option for Team Sky.
"It's up and down the whole time, it's proper racing sort of course, so I think it'll be a lot of attacks from, not just from us, but every body else," Thomas said. "[Deceuninck]-Quick-Step, Alaphilippe... I think a lot of people are going to be aggressive. A lot of racing to come."
Thomas laughed about his weight issue over the winter, something he spoke about before Tirreno-Adriatico. He said he had no idea how heavy he became, but indicated it was nothing near 80kg, but perhaps more around the mid-70s.
Now, he is proper shape at around 71 to fight for the Tirreno-Adriatico race overall.
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