Toyota's Jari-Matti Latvala snatched a Rally GB lead of two tenths on the Sunday morning loop, demoting the M-Sport Ford of title hopeful Sebastien Ogier to second.
Latvala - in search of a third Rally GB win - reduced his deficit from 4.4 seconds to 1.7s on the opening stage of the day, Elsi, before snatching a sensational stage win in Gwydir, which is being run as the powerstage.
The Finn recounted a moment on the stage - which was described as "like Monte Carlo" by Hayden Paddon, referring to how slippy it was - where his car was sideways over a crest and he was uncertain of his fate, but he held on to unseat Ogier.
On the loop's final stage, Great Orme Llandudno, Ogier raced into the town's streets and stole time back from Latvala to end the morning just 0.2s behind with two stages remaining - one gravel and one asphalt.
Esapekka Lappi started the day with a stage win on Elsi to move into a podium spot, and sits 17s behind Ogier.
Lappi's cause was helped by a half-spin for Craig Breen on the powerstage and another mistake in Llandudno. The Citroen man now lies fourth, 27.6s behind Lappi.
At the start of the day Hyundai had Andreas Mikkelsen and Hayden Paddon ahead of Thierry Neuville in eighth, leading some to speculate Hyundai could employ team orders to jump the Belgian ahead of his team-mates for more championship points.
But that was made more difficult by Mikkelsen leapfrogging Mads Ostberg for fifth on the powerstage, and the manufacturer now has to choose between leaving Mikkelsen free to attempt to bag more manufacturer points in the fight with Ostberg, or aiding Neuville's title bid by swapping them around.
At the end of the loop, Mikkelsen and Ostberg lie tied for fifth after Mikkelsen hit a bale and a lamppost in the Great Orme Stage, which allowed Ostberg to claw back time.
Neuville moved ahead of Paddon on the last stage of the loop to take seventh from his team-mate.
Latvala's powerstage win cost his team-mate Ott Tanak dearly; the Estonian retired on Saturday after ripping his sump guard off in Sweet Lamb Hafren (SS16), exposing his radiator which suffered damage.
With powerstage points vital with rivals Ogier and Neuville set to score overall points, Tanak took four for second while Ogier took three and Neuville two respectively.
If the results remains the same, Neuville would hold an 11-point lead over Ogier, with Tanak a further four points back. Ogier started the weekend 23 points behind.
The powerstage is not in its usual slot as the last stage of the rally this year, as the organisers have employed new UK closed-road legislation to have the cars finish the Great Orme stage in Llandudno.
The FIA wanted the powerstage to be representative of the event - on gravel - so the Gwydir test was bumped up to powerstage status.
The drivers now get a fresh set of tyres before another run of Gwydir and Great Orme Llandudno.
Impressive 18-year-old Finn Kalle Rovanpera maintained a lead of over a minute in WRC2 in his works Skoda Fabia R5.
Pontus Tidemand bent an arm after clipping a bank in Gwydir, but carried spares in his car and holds second over British M-Sport driver Gus Greensmith.
Leading positions after SS21
|1||Jari-Matti Latvala, M.Anttila||Toyota Gazoo Racing WRT||Toyota||2h52m42.6s|
|2||Sebastien Ogier, J.Ingrassia||M-Sport Ford WRT||Ford||0.2s|
|3||Esapekka Lappi, J.Ferm||Toyota Gazoo Racing WRT||Toyota||17.2s|
|4||Craig Breen, S.Martin||Citroen Total Abu Dhabi WRT||Citroen||44.8s|
|5||Mads Ostberg, T.Eriksen||Citroen Total Abu Dhabi WRT||Citroen||58.9s|
|5||Andreas Mikkelsen, A.Jager||Hyundai Shell Mobis WRT||Hyundai||58.9s|
|7||Thierry Neuville, N.Gilsoul||Hyundai Shell Mobis WRT||Hyundai||1m05.8s|
|8||Hayden Paddon, S.Marshall||Hyundai Shell Mobis WRT||Hyundai||1m05.9s|
|9||Kalle Rovanpera, J.Halttunen||Skoda Motorsport II||Skoda||8m24.8s|
|10||Pontus Tidemand, J.Andersson||Skoda Motorsport II||Skoda||9m49.6s|
|1||Jari-Matti Latvala, M.Anttila||Toyota Gazoo Racing WRT||Toyota||9m31.6s|
|2||Ott Tanak, M.Jarveoja||Toyota Gazoo Racing WRT||Toyota||0.8s|
|3||Sebastien Ogier, J.Ingrassia||M-Sport Ford WRT||Ford||5.3s|
|4||Thierry Neuville, N.Gilsoul||Hyundai Shell Mobis WRT||Hyundai||5.7s|
|5||Esapekka Lappi, J.Ferm||Toyota Gazoo Racing WRT||Toyota||8.3s|
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