Kirui, this season's Boston marathon winner, clocked 2hr 08min 27sec for gold, 1min 22sec ahead of Ethiopian rival Tamirat Tola.
Alphonse Simbu of Tanzania claimed bronze, just 2sec adrift of Tola after 42km around a 10km Thames river embankment loop in central London in glorious sunshine.
Tola, the Olympic bronze medallist at 10,000m and fastest in the field here with his season's best of 2:04.11, led the field through the halfway point in 1:05.28, accompanied by Kenyans Kirui and Gideon Kipketer, with this year's London champion Daniel Wanjiru a couple of seconds back.
Britain's Callum Hawkins finished fourth in a personal best of 2:10.17, while Kipketer claimed fifth in 2:10.56, a place ahead of Italy's Daniele Meucci, given the same time, a personal best.
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