Kitajima, a double gold medalist in Athens four years ago, put himself halfway toward an unprecedented repeat when he won in 58.91 seconds at the Beijing Olympics on Monday morning. Kitajima's time shattered the previous world record of 59.13 set by American Brendan Hansen in August 2006. Kitajima had set the mark in 2003 before Hansen first broke it a year later.
After seeing his time posted on the scoreboard at The Water Cube, Kitajima thrust his fists in the air, reminiscent of his exuberant celebrations in Athens.
Norway's Alexander Dale Oen, who had been fastest in the qualifying rounds, finished second in 59.20, with France's Hugues Duboscq third in 59.37.
Hansen, who was second at the turn, had to settle for fourth in 59.57.
The event was expected to be a showdown between Kitajima and Hansen, who had not been defeated since losing to Kitajima in Athens and had the fastest time of the year in the world coming into Beijing.
But it was Oen who was the swimmer to beat after setting consecutive Olympic records in the preliminary round and semifinals.
Oen had a slight .12 second lead coming off the turn, but Kitajima poured in on down the stretch to touch first and add another chapter to the story of his sparkling career.
The 100 breaststroke is considered the weaker of Kitajima's two events and prospects are high that he can complete the double when the final of the 200 race is held Thursday.
Meanwhile, a short time earlier, Zimbabwe's Kirsty Coventry set a world record in the semifinals of the women's 100 backstroke, clocking 58.77 seconds to cut .20 off the previous mark set by American Natalie Coughlin in July.