Ennis had the 11-year-old national record of former Olympic champion Denise Lewis in her sights after winning the 100 metres hurdles and high jump and setting a personal best over 200m on day one of the Hypo Meeting.
That gave her a total of 4,097 points - 17 more than at the same stage of the European Championships last year, where she went on to record a personal best of 6,823 - and just eight behind the score Lewis achieved in Talence, France in 2000.
A solid 6.37m in the long jump yesterday morning kept the 25-year-old in the hunt with 5,062 points, just three less than at the same stage in Barcelona.
A best of 43.83m in the javelin left her needing an unlikely time of two minutes 05.70 seconds in the final event, the 800m, and although that proved out of reach, she posted another personal best.
Canada's Jessica Zelinka had overtaken Ennis at the end of the first lap and looked like holding on for the win, but Ennis took advantage of a tiny gap down the inside in the final 10 metres to cross the line in two minutes 08.46secs - almost a second and a half better than her previous best.
A winning total of 6,790 was just 33 below her personal best and considerably more than her target of 6,500 - a fine achievement considering she had missed seven weeks of full training earlier this year with an ankle tendon injury which forced her to skip the European indoor championships in Paris.
Ennis admitted on Friday that she had become increasingly concerned with the injury, which "came on overnight" in training and has still not been fully diagnosed.
However, there was little sign of that over the weekend as she ended up winning by 251 points from Russia's Tatyana Chernova, with France's Antoinette Nana-Djimou another 130 points adrift in third.
A delighted Ennis said: "I'm so glad that's over. I think I'm actually in the best running shape of my life considering I missed so much. I think some of the technical things were off, but I'm so pleased and really surprised.
"I didn't for one minute think I could score that and win as well.
"I'm always nervous before a heptathlon and just before that 800m I thought I could either be sick or cry. I'm so relieved now it's done and I'm happy with my performance. I've done what I set out to do and I couldn't ask for much more really.
"It's a massive relief and my ankle feels brilliant so that's really positive."Ennis admitted it had been something of a gamble to put her unbeaten record on the line at the weekend, but added: "I always wanted to come but then halfway through my injury I started to think there wasn't enough time to be ready.
"I had about six weeks to prepare and that's about the bare minimum you'd need. I didn't want to come and produce a poor score and send out the wrong message with the world championships this year.
"It was a bit of a gamble, but as I started training I was in quite good shape and running well so I knew I could get myself in reasonably good shape and the gamble paid off.
"It's given me so much confidence. Now I know that if I have an injury I can get myself into shape in six weeks and that's good for this year and next year.
"I know people like (sixth-placed Olympic champion Nataliya] Dobrynska will come out a different athlete at the world championships, but it's given me that confidence. I know can get myself in even better shape."