Despite failing to press home her advantage, the 7000-point barrier achieved by only three women is in sight, as is Carolina Kluft's European best of 7032 points.
A lifetime best in the 200 metres (an improvement by five hundredths of a second) of 22.83 seconds restored her lead after a hint of vulnerability, and gave her a lead of 184 points and a career-best first day total of 4158. In second place is Lithuanian Astra Skujyte (3974) with Canada's Jessica Zelinka third (3903), Lyudmila Yosypenko (3902) fourth, and Hyleas Fountain fifth (3900).
Her principal rivals were left well behind. They include US defending silver medallist Fountain, Russia's world champion Tatyana Chernova and Ukraine's Olympic champion Natalia Dobrynska in ninth and 10th. However, they may be best equipped to challenge Ennis, on 3849 and 3835 points respectively, but a decent javelin today should secure the Sheffield athlete the gold.
Only average performances in high jump and shot putt had seen Ennis lose the lead. Skujyte had the measure of her in both, clearing 1.92m in the high jump and launching the shot to an Olympic heptathlon record of 17.31m. Ennis had only cleared 1.86m at the third attempt, but regained the lead on a chilly evening with the 200m.
"To end with a PB in the 200m was brilliant. I think it's a combination of a hard, fast track – obviously, it's the Olympics – and having this crowd behind everyone makes all the difference," said Ennis. "I knew I was in good shape, but to be honest I couldn't imagine performing like this. I've definitely exceeded my expectations. I just want to be having three really solid performances [today] and doing what I know I'm capable of."
Skujyte does not have the armoury to damage her on day two. Ennis's first-day total is 78 more than when she set the British record of 6906 in Gotzis.
The first day of track and field seized the public imagination. Before 8am there were queues 10 metres wide and nearly 100m long for trains to the Olympic Park from central London, but there was hardly an empty seat to be seen in the 80,000-capacity arena by the time Ennis stepped on to the track to a deafening ovation at 10.25.
The president of the world governing body, Lamine Diack, said: "I do not remember the last time this happened and it shows the great affection Britain has for our sport."
Ennis, 2009 world champion and this year's world leader, laid down an indelible marker with her opening run, smashing the British record for the individual 100m hurdles with 12.54sec, the fastest time ever recorded in a heptathlon.
This time would have won the Olympic hurdles title every time since the event was extended from 80m in 1972, with the exception of 1988 and 2004. Ennis is also entered for the hurdles, and her time equalled the third-best in the world this year. She will have until Monday morning to recover for the opening round but is unsure whether to start.
Her team-mates, Katerina Johnson-Thomson (3769, with three personal bests) and Louise Hazel (3427) are 14th and 34th respectively.
Poland's Thomas Majewski became the first repeat Olympic champion since Parry O'Brien (1952 and 1956) with 21.89m. He beat Dave Storl, eight years his junior at 22, by just three centimetres. The lights went out for the so-called Blackpool Tower, 6ft 10ins convicted drug cheat Carl Myerscough. He was 29th of the 40 starters with 18.95m.
Alex Smith finished 10th in the hammer qualifying, reaching tomorrow's final with 74.71m which surpassed the best British Olympic performance by Edinburgh's Chris Black, in 1976. Smith's father, Dave, was Commonwealth champion in Edinburgh in 1986. Smith threw further than his father at the Seoul Olympics in 1988, but dad still has the furthest throw in the family. "Until I get that, he still has room to give me stick."
Tirunesh Dibaba of Ethiopia retained the 10,000m title in 30min 20.75sec while Jo Pavey, at 38, ran the best time of her life (30:53.20). Julia Bleasdale was right behind (30:55.63), a time which is also a lifetime best.
Lee McConnell, the first Scot in action, survived a hot 400m heat, roared home in 52.23 as she defeated Sweden's European champion Moa Hjelmer, who failed to advance. The Glasgow woman qualified all right, but was second slowest of the 24 semi-finallists who line up today.
Olympic champion Christine Ohuruogu (50.80) was fourth fastest, and Shana Cox took third in 52.01 putting. All three UK women are in tonight's semi-finals at 8.05pm.
McConnell said: "Hopefully I'll go faster next time. The atmosphere has helped the British athletes perform today."
But she could scarcely believe coming to the Olympics and on a day more suited to Glasgow's Scotstoun as the sky blackened and rain gusted in. "We were told in second call," she said. "It's where the athletes assemble before marching out. It was dry when I went in, so I didn't have any waterproofs, then I was told it was bucketing down. But there was blue sky when I ran. The track was a bit under water, but it was fine."
Last in Ohuruogu's heat, 30 seconds behind, was the Somalian flag-bearer, Zamzam Mohamed Farah, the only woman in their team. Her national stadium is unuseable, and when fighting was at its peak, she trained in the road – wearing long pants, with head covered – despite the heat.
"We still had to train and run, getting up early in the morning, running past road blocks manned by armed militia. Sometimes the soldier on guard would mistake us for being suicide bombers or attackers. They would order us to stop, or they would shoot."
All three British competitors, led by athletics captain Dai Greene, are through in the 400m hurdles. World Indoor triple jump champion Yamile Aldama, aged 39 and in her fifth Olympics – but first for Britain – qualified for tomorrow's final with her first throw, 14.45m, while in the men's long jump Greg Rutherford and Chris Tomlinson qualified in fourth and fifth (8.08m and 8.06).
Carmelita Jeter was fastest qualifier for the women's 100m semis today with 10.83 as six women broke 11 seconds.
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