The 33-year-old Ethiopian, now concentrating on the roads after a track career that has earned him a fistful of gold medals and world records, has been an ebullient figure in the race hotel this week. With Tergat missing, Gebrselassie has the perfect opportunity to claim his first London title after an ideal period of preparation.
He set a world record of 58min 55sec for the half-marathon in Phoenix in January, and last month he claimed a world record for 25 kilometres in the Netherlands, recording 1hr 11min 37sec.
Although other dangerous runners remain - notably Kenya's defending champion Martin Lel, his fellow countryman Evans Rutto, Morocco's Jauad Gharib and the former world record-holder, Khalid Khannouchi of the United States - Gebrselassie can afford to be confident as he utilises the experience gained on this course in making his marathon debut in 2002.
On that occasion, he finished third behind Khannouchi and Tergat, despite a superb time of 2hr 6min 35sec.
"In 2002 I ended up being the pacemaker for almost 40km," he said. "That won't happen this time. I will treat it more like a championship. I was very new at marathon running then and to be honest I thought it would be easy. So I ran faster and faster and, of course, at the end, I was very tired.
"42km is a long way. You never know what can happen. I have learned to be patient. Also, in 2002 I made the mistake of only drinking water, but this year I will be taking carbohydrate drinks. I've learned that when you run marathons it's not like running the 5,000m or the 10,000m. It needs attention."
That is a lesson that resonates through the whole event and James Cracknell, recently back from his transatlantic row, will be running his first marathon alongside his colleagues from the triumphant Olympic rowing four of 2000, Sir Steve Redgrave and Sir Matthew Pinsent.
Paula Radcliffe's foot injury has prevented her making an early impact in the two-year World Marathon Majors series, which began with this month's Boston Marathon and offers the best male and female runners $500,000 (£280,000) each.
The women's race looks a close call between the pair who contested the recent Chicago race, Deena Kastor of the United States and Romania's Constantina Tomescu-Dita, although Kenya's 2004 winner Margaret Okayo could beat both if her back injury allows.
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