In a soaking chill reminiscent of a summer evening in his valleys of his native land, Geraint Thomas became the first Welshman to wear the yellow jersey of the Tour de France, finishing five seconds ahead of the young Swiss Stefan Küng at the end of the 14 kilometres. That feat in itself would have been enough to get Chris Froome’s quest for a fourth Tour off to a flying start but the triple winner gained significant time on all his rivals.

Thomas’s victory crowns a distinguished career that has included Olympic gold medals in Beijing and London, and it compensated for the unfortunate end to his assault on the Giro d’Italia in May, when he was forced out after a heavy crash involving a motorbike. There had been inevitable questions about his form after that incident but this appears to resolve those doubts. Ironically for a rider who has seen his chances dashed numerous times by ill-timed crashes, and who finished the Tour in 2013 with a broken pelvis, Thomas stayed upright on a day when the wet conditions played a defining role.

The 31-year-old former member of the Maindy Flyers became only the eighth Briton to wear the yellow jersey. He took full advantage of a rising wind that blew a little more strongly against later starters including Küng and the big favourite, the reigning world time trial champion, Tony Martin, who had been expected to deliver a home victory but fell short by eight seconds.

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“This is good for my morale and good for the team,” said Thomas, who claimed he was inspired by watching the Lions beat the All Blacks earlier in the day. “I’m buzzing off that, it took my mind off the race. I took the first corner quick, was told to take it easy so took no big risks. I tried to save it for the last four kilometres and couldn’t have gone any better. Froome showed his horsepower, as he was taking it easy on the corners. The goal for the team won’t change, though, it’s all about him so if I have to lose the jersey, so be it.”

Throughout the day, the rain fell on Düsseldorf with gentle relentlessness. The barriers became a sea of umbrellas, the tarmac a treacherous skating rink, turning the stage from a straightforward blast up and down the east bank of the Rhine into the cycling equivalent of Russian roulette. The equation for each of the contenders was simple and brutal: gamble on gaining time on the rest and risk a crash that would at best compromise the first part of the Tour or at worst end it completely.

Froome had followed Thomas in a team car to look over the course one last time; he not only emerged unscathed but gained valuable time on his rivals for the overall classification, even his former team-mate Richie Porte, who lost 35sec to the defending champion. The Australian Porte said afterwards: “I was nervous, tense, super careful on the corners. It wasn’t my best time trial.”

Play Video 0:29 Geraint Thomas: 'It's just an amazing feeling' – video

Apart from Froome, most of the favourites finished closely grouped together, indicating that they had all taken the corners at a similar cautious pace. Simon Yates dropped only 25sec in a discipline that he does not regard as his strong suit but Nairo Quintana, Alberto Contador, Thibaut Pinot, Romain Bardet and Jakob Fuglsang finished between 36 and 42 seconds slower than Froome. These are not conclusive gaps – although who knows how tight this year’s Tour will prove to be – but the pressure is on those who want to unseat the Team Sky leader with only 16 minutes raced.

Time-trialling in the wet is difficult enough but on an urban course it can turn into a nightmare. The riders had to contend with lengthy puddles in dips in the tarmac, pedestrian crossings picked out in a type of red-dyed tarmac with all the adhesion of a patch of ice, narrow turns that were hard to read, with soaking, slippery white lines on the entrances and exits. For most of the riders, this was a stage to get through, with the 13 corners to be negotiated with extreme care in the sodden conditions.

The fate of Alejandro Valverde showed the potential cost of a second’s inattention or over-ambition. The near-veteran Spaniard, one of the few survivors of the Operación Puerto blood-bag scandal still racing, had enjoyed a quite brilliant early season and had been expected to be a strong second foil for Quintana in the coming weeks. His Tour came to a sudden halt on day one with a sickeningly heavy fall on the sweeping left-hander off the second bridge over the Rhine with just under seven kilometres to ride. He departed the race with lower leg injuries including a broken knee cap. Another Spaniard, Bahrain-Merida’s 28-year-old Jon Izaguirre, fell on the same corner and was also put out of the race.

Not surprisingly, many were reduced to walking pace as they tried to start their Tours by remaining in one piece. The first to crash was the Dutch sprinter Dylan Groenewegen, followed by his team-mate Primoz Roglic – an outside chance for the stage win; while the Frenchman Tony Gallopin also came a cropper, as did Team Dimension Data’s British Tour debutant Scott Thwaites. Gallopin was taken to hospital with contusions to his shin; Thwaites had merely the usual grazes.

Thomas has enough time in hand on the sprinters to hold the jersey at least as far as Monday’s hilly finish in north-eastern France, but on Sunday he and the others face 203km in the saddle south-west to Liège, largely flat and probably ending in a bunch gallop, where Mark Cavendish will face his first real test after his recovery from glandular fever.