He finished ahead of Richard Allen and Richard Jones after the organisers had encountered problems coping with the largest Olympic-sized triathlon in Europe.
They had not counted on the huge number of amateur competitors, who had to be ushered off the course to allow the elite athletes through.
However, this did not distract Lessing, who extended his lead with every stage. After the swim he was 10 seconds ahead, he had increased his advantage to 1min 30sec after the cycle ride and by the end of the run he was a massive 2:30 ahead of the chasing pack.
"What was really pleasing is that this came off the back of a really hard series of eight races in nine days, which made this one really tough," he said.
"I led from the front and I had to keep my mental toughness going so that I could push myself right to the very end. That was the major pleasing factor about this performance.
"I was surprised that I was so far in front during the cycling. I thought that with everyone else slip-streaming each other, they would catch me. It's hard to lead from the front, but the winning makes all the toughness of a race like that disappear."
Lessing is convinced that despite yesterday's problems, the London site will develop into one of the greatest triathlon areas in the world.
"It's a bit windy in the dock, but over the next couple of years I am sure the event will become really big in terms of the names it attracts," he said.
"It was great to see so many people lining the various streets and I think it can only get bigger."
There was also a one-two for Britain in the women's event, Loretta Sollars being followed home by the 19-year-old University of London student Jessica Harrison.
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