Hiroshima's Brazilian striker Douglas took advantage of confusion between Kawasaki goalkeeper Shota Arai and defender Shogo Taniguchi to score in the third minute.
The 2012 and 2013 champions then protected their lead to move to 22 points from 10 games.
FC Tokyo remained second behind the Reds after Yoshinori Muto struck a brace in their 3-2 win against Vegalta Sendai on Wednesday.
Masato Morishige opened Tokyo's account in the 34th minute and Muto twice found the net in the second half in what looked like a one-sided match.
A counter-attacking Sendai scored two late goals, however, through Naoki Ishikawa and Ramon Lopes and Tokyo survived some anxious moments before winning the match to take their tally to 23 points from 10 matches.
Urawa lead the standings with as many points, having played one game less.
In other matches, Shimizu S-Pulse's 2-2 home draw with Sagan Tosu stretched their winless run to nine league matches. (Reporting by Amlan Chakraborty in New Delhi; editing by Justin Palmer)
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World 20.08.2018Celebrating the African diplomat legend
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