Ott Tanak stormed into the Rally GB lead on Friday night's stages, leaping from fourth to first while erstwhile leader and Toyota World Rally Championship team-mate Kris Meeke fell back.
Tanak benefited from running first on the road for Dyfnant, winning the stage by 5.7 seconds from Hyundai's Andreas Mikkelsen in near-daylight conditions as drivers behind ran in increasing darkness.
Luck was also on Tanak's side as damaged wires meant his lights weren't working on Dyfnant and required roadside repairs to get them restored for the fully-dark Aberhirnant test, which he also won.
Reigning champion Sebastien Ogier went third-quickest on both evening stages to cement his second place, despite dropping behind the charging Tanak.
Ogier was down to third after going 5.8s slower than Tanak on Dyfnant but quickly retook the position from Meeke by only 0.2s, as the former leader complained of aquaplaning causing a "big slide" on Aberhirnant.
Thierry Neuville conceded time to both his championship rivals in the night, the Hyundai man suggesting Tanak had benefited from clear daylight as he struggled to constantly adjust his lights on Dyfnant when he got there.
Four seconds were lost to Ogier and a few tenths were also lost to Meeke across the pair of day-ending tests, leaving Neuville 4.8s behind Meeke in fourth overall.
Due to a 20 minute delay to the night-time loop's pair of stages - caused by an earlier stoppage on the re-run of Penmachno due to Jari-Matti Latvala's crash - Dyfnant quickly descended towards darkness for WRC runners further down the order.
As last WRC car on the road, Craig Breen suffered most. He was the only driver aside from M-Sport's third driver Pontus Tidemand to clock a time over 10s slower than Tanak on Dyfnant.
That allowed Breen's Hyundai team-mate Mikkelsen to take fifth and left Breen within range of seventh-placed Teemu Suninen, though he gained a few tenths on Suninen on Aberhirnant to end Friday 3.9s ahead in sixth.
Eighth-placed Elfyn Evans, who had lost over 40s in the morning with suspension damage, cut four seconds out of Suninen's advantage, while Tidemand ensured M-Sport finished the day with its cars in formation by moving into ninth.
Those positions had been gifted to him through misfortunes for the leading WRC2 Pro contenders, however, as Kalle Rovanpera lost over a minute with a puncture on Dyfnant and Gus Greensmith retired before the same stage with a technical issue.
Leading positions after SS10
|1||Ott Tanak, M.Jarveoja||Toyota Gazoo Racing WRT||Toyota||1h14m30.8s|
|2||Sebastien Ogier, J.Ingrassia||Citroen Total WRT||Citroen||3.4s|
|3||Kris Meeke, S.Marshall||Toyota Gazoo Racing WRT||Toyota||3.6s|
|4||Thierry Neuville, N.Gilsoul||Hyundai Shell Mobis WRT||Hyundai||8.4s|
|5||Andreas Mikkelsen, A.Jager||Hyundai Shell Mobis WRT||Hyundai||25.7s|
|6||Craig Breen, P.Nagle||Hyundai Shell Mobis WRT||Hyundai||33.5s|
|7||Teemu Suninen, J.Lehtinen||M-Sport Ford WRT||Ford||37.4s|
|8||Elfyn Evans, S.Martin||M-Sport Ford WRT||Ford||51.8s|
|9||Pontus Tidemand, O.Floene||M-Sport Ford WRT||Ford||2m56.6s|
|10||Jan Kopecky, J.Hlousek||Skoda Motorsport||Skoda||4m01.1s|