Barring an accident in the procession to the Champs-Elysees on Sunday, the 32-year-old Welshman will give the team their sixth title in seven years after Bradley Wiggins in 2012 and Chris Froome in 2013, 2015, 2016 and 2017.
Froome had been the favorite to retain his title but he paid the price for the efforts he had put into winning the Giro d’Italia in May as he just failed to become the first man in 20 years to achieve the Giro-Tour double.
He took second place in the 31-km time trial, from Saint-Pee-sur-Nivelle, won by a solitary second by time-trial world champion Tom Dumoulin, with Thomas coming home third, 14 seconds off the pace.
Overall, Thomas leads Dumoulin by 1:51 and Froome by 2:24 after the lanky Briton leapfrogged Slovenian Primoz Roglic, who cracked in the last competitive stage before Sunday's traditionally unchallenged final leg.
Thomas topped the provisional rankings at the first checkpoint but the Briton rode cautiously to the line, taking no risks on sometimes slippery roads to all but secure his first grand tour title.
He posed for cameras with his national flag and Dave Brailsford, the man behind all of Team Sky’s Tour de France victories, who was brought up in Wales.
“It has been a great race - if we look at all our individual riders they are amazing,” Thomas said.
“It’s just a whirlwind. There was a massive emotion across the line. It’s going to take a while to sink in, for sure,” Thomas told a news conference.
“I’ve been staying in a bubble - I have no idea what it’s like. It’s insane, really. It’s going to take a while (for me to realise).”
Froome, who started the race as team leader, came close to another stage win but eventually had to concede defeat to Dumoulin. But he at least salvaged a podium finish after dropping to fourth overall following Friday’s last mountain stage.
Stage winner Dumoulin said: “It’s an amazing day. It was stressful, though, because this morning I could not find my (world champion) rainbow jersey suit and I had to ask my sponsor to give me a new one at the last minute. What a crazy day.”
A gracious Froome told reporters: “It’s a dream to finish on the podium with Geraint. It’s incredible after a very hard day yesterday.
“I wouldn’t have thought it was possible after yesterday. I’m really happy.”
HAPPY TO SURVIVE
France’s Julian Alaphilippe and world champion Peter Sagan, of Slovakia, both finished within the time cut and are set to claim the polka dot jersey for the mountain classification and the green jersey for the points classification, respectively.
“Yesterday was so hard. I’m happy I survived it,” said Sagan, who crashed heavily in a descent on Wednesday.
“Today was OK and tomorrow is the end of the Tour.”
Frenchman Pierre Latour will finish 13th overall and will clinch the white jersey for the best under-25 rider.
