Kebede, who was not selected for London 2012, overhauled his Kenyan rival Emmanuel Mutai in the final kilometre to win in two hours, six minutes, four seconds and must surely have secured a place on the list for August's world championships in Moscow.
"Many athletes ran 2:04, because of that they selected them (for the London Olympics)," Kebede said.
"In October I went away, won (in Chicago), ran a personal (best) time (2:04:38) and now I win again this competition," he added.
"I'm happy. Maybe I think I'll run in the world championships," the Ethiopian, also champion in 2010, said with a smile.
Jeptoo had, at least, made it to the London Games but was pipped to women's marathon gold by Ethiopia's Tiki Gelena by five seconds. This time, though, the Kenyan was not prepared to race it out at the end of the 42.195km slog around London and after pushing the pace at around 30km, she ran solo up The Mall to win in 2:20.15.
The injection of pace proved too much for Jeptoo's only companion, world champion and compatriot Edna Kiplagat, who began to lag and finished more than a minute behind.
Gelena, making her debut in the London Marathon, came a cropper after colliding with a wheelchair racer at a drinks station at 15km and did not feature among the leaders after halfway, and finished 16th – her shoulders rolling as she laboured to the line.
Men's Olympic champion Stephen Kiprotech of Uganda had a disappointing debut, finishing sixth after struggling to keep up with the blistering pace set in the first half of the race, which put paid to world-record holder Patrick Makau, who was 11th.
Britain's double Olympic track champion Mo Farah kept up with the leaders until halfway, before dropping out as planned soon after crossing Tower Bridge.