The Nagoya Diamond Dolphins scored a difficult 86-80 victory against fellow contender Alvark Tokyo on Wednesday at Arena Tachikawa Tachichi.
Ray Parks Jr. scored 10 points to go with 4 rebounds and 1 assist for Nagoya, which improved to 21-9.
The Diamond Dolphins now occupy the second spot in the B.League West division.
With the loss, Tokyo dropped to 21-8.
Elsewhere in Japan, Kobe Paras ended a scoreless spell by firing 16 points for Niigata in their game against Hokkaido.
Ten of his total points came in in the first quarter.
However, it was not enough to save the Albirex which got walloped by Levanga, 107-85.
It was Niigata's 26th straight defeat in 29 games. Hokkaido improved its record to 12-17.