Brazilian striker Emerson fired a hat-trick for the Reds to take his tally for the season to a league-best 27 goals.
Urawa won the second-stage title at the weekend and play Japanese champions Yokohama F-Marinos in the two-leg J-League final on December 5 and 11.
The Reds coached by former German World Cup winner Guido Buchwald improved to 34 points from 14 games after overpowering 10-man Reysol.
Injury-troubled Yokohama who won the first-stage title lost 2-1 to Albirex Niigata at International Stadium and slipped to sixth with 22 points.
South Korea internationals Ahn Jung-hwan and Yoo Sang-chul as well as Japan striker Tatsuhiko Kubo are all sidelined for Yokohama with long-term injuries.
At the foot of the table Cerezo Osaka staved off relegation at least until the weekend with a 2-1 victory at home to Shimizu S-Pulse.
Cerezo's city rivals Gamba Osaka won 2-1 at former champions Jubilo Iwata to stay second on 27 points with one match remaining in the second stage.