Yamauchi, who was contesting her first marathon since that feat after injury wrecked her hopes of competing in last summer's World Championships, admitted she was disappointed with the outcome.
Her preparations were hardly helped by a gruelling six-day journey from the United States after disruption caused by Iceland's volcanic eruption.
She saw her hopes of a podium finish dashed when the field, led by eventual winner Liliya Shobukhova, flew past her almost at the halfway point but she stuck resolutely to the task of completing the course.
"I was just thinking 'try and hang on' but they came past me quite quickly," said Yamauchi.
Yamauchi still clocked a very reasonable two hours 26 minutes 16 seconds but admitted to momentarily considered dropping out. The 36-year-old Oxford born athlete said: "When I got dropped from the group I was thinking 'I'm not going to close this gap. Is there any point?'
"But then I thought a lot of the runners were good half marathon and 10km runners but there was a question mark about the marathon.
"So I thought 'I've got to keep going.' Had I run a couple of minutes quicker and come fifth then that would have been a really good result."
The Japan-based star is adamant that she can bounce back for the 2012 London Olympics which remains the major target in her future plans.
"I hope now I can train injury free through the summer and by the autumn be back to the form I was in London last year."
Russia's Shobukova, third last year, scored a solid victory in 2hr 22 minutes from compatriot Inga Abitova with Ethiopia's Asselefech Mergia third.
Last year's runner-up, Ethiopian Tsegay Kebede, scored a runaway win in the men's event, missing the course record by just nine seconds in a time of 2hr 5min 19sec.