The defending champions' win in a thrilling rematch of last season's championship decider leaves Saitama Wild Knights as the sole unbeaten side in the premier division of Japan Rugby League One after they edged Tokyo Sungoliath 31-30 on a dramatic weekend.
Based in Japan since the 2023 Rugby World Cup, Mo'unga is headed back to New Zealand rugby after the Japanese club season.
The 31-year-old flummoxed three defenders with quick feet to dive across for the match-winner in the final play of an epic contest.
Toshiba Brave Lupus led 12-3 at halftime but conceded a try to Shaun Stevenson shortly after the re-start.
The inform New Zealand fullback then set up winger Yamada Hibiki 20 minutes later, allowing the Spears to claim the lead for the first time.
The scores were tied 17-17 heading into the final stages, and Kubota appeared to have won it when ex-Wallaby flyhalf Bernard Foley landed a penalty goal with three minutes left.
But Toshiba gained the field position that provided Mo'unga with the opportunity to conjure up the winning play.
The Wild Knights looked to have done the business against Tokyo Sungoliath when they worked to a 31-16 lead with less than 10 minutes remaining.
Sungoliath narrowed the gap to a point after Springboks winger Cheslin Kolbe partially redeemed himself for an earlier yellow card by crossing for a try with two minutes to play.
But Wild Knights held on, with their sixth win of the season moving them three points clear on the standings
The end to Kubota's unbeaten streak allowed third-placed Kobelco Kobe Steelers to close their standings gap to a point following their 38-32 success against bottom side Yokohama Canon Eagles.
Former All Blacks second rower Brodie Retallick, the competition's leading try-scorer, scored his eighth of the season during the Steelers' success.
The Eagles remain stranded at the foot of the standings and are the only side still to win in Division One after Mie Honda Heat got off the mark following a rousing 32-23 win over Urayasu D-Rocks at Tochigi.
The maximum point return took Honda above both Toyota Verblitz and Mitsubishi Sagmihara Dynaboars on the standings,
Sagamihara were architects of their own demise to some extent during their 33-24 loss to BlackRams Tokyo, blowing a 19-13 halftime lead, as well as conceding two yellow cards during the second half.
Shizuoka BlueRevs climbed into the top six, while leaving Verblitz languishing in the relegation series places after an impressive 43-19 demolition job at Yamaha Stadium.
