"I woke up late [and I thought] I'm going to miss the bus," he recalled to the BBC in a recent interview.
Farah, who is coached by marathon legend Alberto Salazar, was using the London Marathon as a test run before he commits to the full distance next year.
"The biggest challenge [during the race] is picking up the drinks and making sure you pick up the right drink," he admitted. "I made a mess of it. At one point I had to stop and go back for it. Things like that don’t help as you want to save energy."
In the race, Farah was able to match wits with the lead pack. They ended up going out ridiculously fast–at world-record pace in the opening half.