Thomas attacked a group of favourites within six kilometres to race and pulled in the last remaining man, Mikel Nieve (Mitchelton-Scott), in the final 500 metres. Froome, four time Tour winner, attacked behind his team-mate and closed within 20 seconds.
“I think it was a bit of a spur of the moment thing for us but it made sense, it was perfect, we didn’t even have to talk,” Froome said of Thomas’s move.
“It was the right thing for G to do. To push on there. I let the wheel go because I knew the onus would be on the rest of the guys to chase.”
Froome finished his warm down while Thomas celebrated in the yellow jersey at the top of the climb, 1,885 metres up in the Alps. Thomas was last in this position when he won the opening time trial last year in Düsseldorf and wore the yellow jersey for four days.
“Absolutely fantastic,” Froome added, “he’s in the form of his life and fully deserves it.”
Thomas leads the race by 1-25 minutes over Froome and 1-44 over Tom Dumoulin (Sunweb). Vincenzo Nibali (Bahrain Merida) is fourth at 2-14 and Primož Roglič (LottoNL-Jumbo) at 2-23 in fifth.
Froome said that his moves behind were to keep rivals like Dumoulin in check and gain time on the others.
Dumoulin attacked on the descent of the Cormet de Roselend after an earlier move by Alejandro Valverde (Movistar). Sky pulled back Valverde, Thomas went on the attack and Froome started his own.
He first made a move with Romain Bardet (Ag2r La Mondiale) and another, more powerful effort that saw him ride free with Daniel Martin (UAE-Team Emirates). Froome dropped Martin just ahead of the the final kilometre and moved in on Dumoulin, who won the sprint ahead of Froome for the second place bonus seconds.
“[Martin] put in a big acceleration and I was surprised I was the only one who was on his wheel. But yeah, Dan has ridden really well. I think he’s trying to make the time back from when he crashed,” Froome said.
“But the main guy who stands out as a threat to us right now is Tom Dumoulin. He rode a very impressive stage today. I guess it depends on how everyone backs up tomorrow.”
Dutchman Tom Dumoulin won the Giro d’Italia in 2017 and placed second behind Froome in the 2018 Giro in May.
“Dumoulin is right up there on the GC now, we couldn’t give him too much room and obviously he is someone who can TT at the end of the Tour as well. We are going to have to keep a close eye on him.”
The 2018 Tour’s run through the Alps finishes with Alpe d’Huez on stage 11 on Thursday; a climb where Froome has never had an easy time.
“I just hope I can get up there, every time I’ve been up the Alpe d’Huez it hasn’t been happy experience for me so if I can turn it around tomorrow it can be fantastic,” Froome said.
“I was hanging on for dear life [when I won the 2015 Tour there], if I can feel better tomorrow, I’ll be a big step in the right direction.”