Jessica Ennis is on target for heptathlon gold after two brilliant personal bests produced her highest score on the first day.

Ennis got off to a phenomenal start, destroying her personal 100m hurdles best by 0.25secs, in the fastest ever time set by a heptathlete in the event.

She then clocked 22.83 seconds in Friday's final event, the 200m, to end the day on 4,158 points, 184 clear of Austra Skujyte in second.

The Sheffield athlete is 255 points ahead of Canadian Jessica Zelinka in third going into Saturday's final three events.

More importantly, she leads world champion Tatyana Chernova, expected to be her biggest rival, by 309 points and reigning Olympic champion Nataliya Dobrynska by 323.

Chernova is notoriously strong in the second day's long jump, javelin and 800m, but Ennis's lead is double that of the one the Russian eliminated on the final day in the Daegu World Championships last summer.

It is also the 26-year-old's best first day score by 34 points, and is 45 points up on her total at the same stage when she set her British record in Gotzis earlier this summer.

She told BBC Sport: "I'm so pleased to end the day with that. I knew it was a fast track from the hurdles but I'm made up to have run a PB.

"I'm still in shock about the hurdles but it was a bit up and down. High jump I was a bit disappointed by, but not too bad. Shot put, also a little bit disappointed, but all solid performances and two PBs is brilliant.

Remaining heptathlon events (all times BST) Saturday 10:05 Long jump 11:40 Javelin 20:35 800m

"I'm going to have a really strong day on Saturday and make sure everything is really solid. I'm glad to have got today out of the way and got a good score under my belt, but there's a lot more work on Saturday.

"It's been amazing, the crowd have been unbelievable. I know it sounds cheesy but they really do lift you when come round the bend and hear the roar. It makes a huge difference."

Ennis started Friday with a 100m hurdles personal best and set a new British record in a packed stadium. Her 12.54 seconds equalled the time that Dawn Harper ran to win individual gold for the event in Beijing.

She then cleared 1.86m in the high jump to lead the US's Hyleas Fountain by 25 points and her own British team-mate Katarina Johnson-Thompson by 103, before a less impressive 14.28 metres in the shot put briefly gave Skujyte the overall advantage.

The Lithuanian had produced a remarkable 17.31m, the best mark recorded in a heptathlon, but her 200m is weak and her showing of 25.43 secs saw her relinquish the lead.

Chernova had finished last in her hurdles heat in 13.48 seconds to lie in 15th overall but a high jump of 1.80m, allied to a shot put of 14.17m and better than expected 23.67 in the 200m saw her move up to ninth.

And Dobrynska, who lost her husband to cancer in March, struggled in the shot and was more than two metres down on her best.

Britain's Louise Hazel, Commonwealth champion, lies down in 34th after a poor high jump, but her 19-year-old compatriot Johnson-Thompson - newly crowned world junior long jump champion - sits in 14th on 3,769 points, on track to set a junior world record.

Johnson-Thompson began the biggest competition of her life with a fine 13.48 seconds to equal her personal best in taking fourth in heat four.

Analysis Denise Lewis Heptathlon gold medallist and BBC Sport analyst "She still needs to do a lot of work on Saturday, and that long jump is a crucial event. That could be a turning point. But she is in the perfect spot at the moment. That 200m to finish was just what she needed. You have to remember these girls are very tired by the end of the day. But the track is quick and she did exactly what she needed to do."

And she went even better in the high jump with another PB, this time 1.89m, as the partisan crowd of 80,000 - almost unheard of for a morning session of athletics - roared the British athletes on.

But it was Ennis who sent the capacity evening crowd into raptures as she stormed down the home straight in the 200m.

On the basis of their respective PBs, she needed a lead of 250 or more points going into Saturday to hold an advantage over Chernova.

When she beat the Russian to the European title in Barcelona two years ago that margin was 299; when she lost her world title last summer, it was 151.

Although she has struggled at times with her long jump this summer, that lead this time of 309 gives her a wonderful chance of sealing the greatest triumph of her career.