Riley won the man-of-the-match award on Sunday after scoring two of the Wild Knights' eight tries as they exacted revenge for their two-point loss to the Spears in last year's title decider.
The 26-year-old played for the Australian Under-20s in 2017 but was unable to secure a Super Rugby contract with the Reds.
His first try came after he collected a delicate chip from Brave Blossoms' flyhalf Rikiya Matsuda; the second from supporting a midfield bust by the former (Waikato) Chiefs backrower, Lachlan Boshier.
After leading the try-scoring in the maiden edition of the league two years ago with 13, Friday night's haul took Riley to third on this season's standings, with 10.
Now a Japanese international, the 18-cap centre has scored 26 tries from 40 appearances in the league.
Eleven of those games have been this season, each of which have been won, with the latest victory moving the Robbie Deans-coached Wild Knights to within one of semi-final qualification, while leaving the Spears' title defence in tatters.
Richie Mo'unga's Brave Lupus Tokyo remain second, surviving a scare on Sunday against Black Ram Tokyo, winning 40-33.
Tokyo Sungoliath are third despite losing in dramatic fashion 37-35 against Yokohama Eagles, capitulating after they led 35-10 at halftime.
A week earlier, Sungoliath had run down a 21-point halftime deficit to beat Toyota Verblitz.
Ironically the Eagles have slipped a point behind Dave Rennie's Kobelco Kobe Steelers on the table despite the win, with the latter moving outright fourth after a bonus point 60-17 win against Quade Cooper's hapless Hanazono Kintetsu Liners in today's Kansai Derby.
In other matches, Steve Hansen's Verblitz virtually conceded any playoff hopes after a 24-8 loss to Shizuoka Blue Revs, in a game notable for the yellow card and penalty try conceded by All Black flyhalf Beauden Barrett for dangerous contact to the head of Blue Revs winger Keagen Faria.
Mie Honda Heat couldn't back up their first win of the season, falling 31-26 to Sagamihara Dynaboars.
