Katarina Johnson-Thompson’s hopes of taking team-mate Jessica Ennis-Hill’s Olympic heptathlon title in Rio were dealt a hammer blow by a woeful shot put performance.
The 23-year-old could only manage a best throw of 11.68 metres to drop from first place to sixth after the opening three events at the Olympic Stadium.
The shot is the Liverpool athlete’s weakest event by far, but this was still a well below-par performance, given she has thrown a personal best of 13.14m this year.
It moved her overall total to 2,904 points, 203 behind Belgian leader Nafissatou Thiam.
Ennis-Hill moved up to second from third, her total of 3,027 putting her 80 behind Thiam, despite only managing a best throw in the shot of 13.86m, down on her best this year of 14.29m.
It meant the 30-year-old, looking to become the first British woman to retain an Olympic title in athletics, two years after the birth of her son Reggie, was well-placed going into the final event of day one, the 200m.
Canada’s world number one Brianne Theisen-Eaton lay in fifth place.
Johnson-Thompson’s struggles make the mouth-watering prospect of a titanic tussle between the two Britons for gold in the 800m, the last of the seven events on Saturday, now unlikely.
The day had all started so promisingly for the British pair - and Johnson-Thompson in particular after she produced a British record clearance - and equal world heptathlon best - of 1.98m in the high jump.
It was some statement of intent from an athlete who was left distraught at last year’s World Championships in Beijing when three fouls in the long jump dashed her medal hopes. She will now be hoping her shot woes have not done the same.
Her team-mate, the defending champion, also got off to a flying start, clocking 12.84 seconds in the 100m hurdles and then clearing 1.89m.
It was her third-fastest time since London 2012 - and her fastest in a heptathlon since then - and her best high jump since before the last Olympics.
Johnson-Thompson, the heir to her compatriot’s multi-eventing throne, had clocked 13.48secs over the hurdles, 0.11s down on her best this year, but a solid enough time given the rainy conditions at the start of the morning.
The Britons were hit by a wall of noise on their first morning of London 2012, a teenage Johnson-Thompson saying ‘wow’ at the roar which greeted her introduction.
There was no chance of that at a near empty Olympic Stadium for the start of competition here, even if the British fans were the ones making the most noise.
There looked to be barely a couple of thousand spectators in the 56,000-capacity venue when the action got under way in the morning and at the start of the evening session it was less than a fifth full.
In the final event of day one, Johnson-Thompson won her 200m heat, with Ennis-Hill second, but it was enough for the Sheffield athlete to lead the field heading into Saturday.