The Wild Knights made it seven wins from as many outings, but were made to work for it in wet conditions as they beat  BlackRams Tokyo 13-6 on Saturday.
Now seventh, the losing bonus point was no more than the TJ Perenara-captained BlackRams deserved as they restricted the Wild Knights to one try.
The league leaders had scored 31 in their previous six matches.
Bernard Foley's Kubota Spears have never lost at Spears Edoriku Field and that record was not put under threat by Urayasu D-Rocks on Saturday, with Samu Kerevi's side succumbing 48-14 despite two tries from Springbok back-rower Jasper Wiese.
The Spears suffered their first defeat against Brave Lupus Tokyo in the previous round, and the defending champions were at the centre of the upset of the season on Saturday when beaten 44-38 by Mie Heat.
Coached by former Italy boss Kieran Crowley, who engineered the Azzurri's first win over an Australian side coached by Dave Rennie, Heat scored five tries in the first half to storm to a 34-21 lead.
The advantage proved decisive, with Brave Lupus needing three tries in the final six minutes to snatch an unlikely bonus point.
Rennie's Kobe Steelers took advantage of the fourth placed side's defeat, claiming maximum points from a 60-45 win over Shizuoka BlueRevs in a frantic 80 minutes that featured 17 tries.
Skipper Brodie Retallick, the competition's leading try-scorer, touched down for the ninth time this season as the Steelers extended their advantage over Brave Lupus on the ladder to five points.
Former All Blacks boss Steve Hansen's Verblitz fell to the foot of the standings after their 20-14 loss to the previously winless Yokohama Eagles.
The Eagles jumped two places on the table, with 11th-placed Sagamihara denied the chance to add to their tally after Sunday's match with Tokyo Sungoliath was postponed because of snow.
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