Toyota World Rally Championship driver Jari-Matti Latvala moved into the lead of Rally Finland on an ultra-close afternoon loop, after which the top four are split by just 2.6 seconds.
Latvala overturned his team-mate Ott Tanak's 5.4s morning advantage with the fastest time on the second pass of Moksi to open up a slender 0.4s lead after the 12.45-mile-long test.
A further two stage wins, on SS9 (Asamaki) and SS10 (Aanekoski) enabled the three-time event winner to build a two-second lead over Kris Meeke, which was marginally reduced after the Harju street stage.
Meeke and Esapekka Lappi also took chunks out of Tanak despite the road conditions worsening with each passing car.
The pair set identical times on stage seven and were evenly matched on the following Urria test which meant all three were tied for second, just 0.6s behind Latvala.
An "apprehensive" run on SS8 cost Meeke time to Lappi, but 2016 winner Meeke moved back ahead of the Finn on the penultimate stage after setting the same time as Latvala.
He is now just 1.2 seconds behind his Toyota team-mate, with the same margin back to Lappi heading into day two.
Running first on the road meant Tanak suffered the most from the increasingly rutted sections of the stages, with the championship leader later dropping behind Meeke and Lappi, lamenting that there was "nothing more I can do".
After a sensational performance on the morning loop, WRC returnee Craig Breen put a loose bonnet pin issue aside to maintain fifth ahead of Andreas Mikkelsen by just 0.4s, with the pair embroiled in an entertaining battle that ebbed and flowed.
Overhauling Citroen's Sebastien Ogier on the opening stage of the afternoon, Mikkelsen was fastest on SS8 (Urria 2) before outpacing Breen by four-tenths in the final two tests.
Breen dropped 1.4s on SS7 with his bonnet partially restricting his visibility but the Irishman fought back to remain fractionally ahead.
Thierry Neuville endured a frustrating day in his Hyundai i20 after topping Thursday evening's opening superspecial stage.
The Belgian struggled with set-up issues in the morning and, despite setting better times in the afternoon, remains somewhat adrift of Ogier in front of him and 30.9 seconds off Latvala.
Neuville's troubles mean he will have to run early in the running order for the remainder of the event, with surface cleaning likely to limit his progress up the standings.
M-Sport's day one struggles continued with Teemu Suninen and Gus Greensmith rounding out the top 10.
Suninen lost time in the morning to a broken splitter on the opening stage with the Finn slipping to nearly a minute off the overall pace of Latvala.
Greensmith had a spin on SS5 but got the better of team-mate Suninen on the penultimate stage of the day at Aanekoski 2, but lies more than 1m30s behind the leaders.
In the WRC2 Pro class, Kalle Rovanpera remains the driver to beat in his Skida Fabia R5; the Finn was fastest on each of the afternoon stages and has a comfortable 2m15.1s lead over Eric Camilli's Ford Fiesta R5.
Pierre-Louis Loubet continued to build his lead in the WRC2 privateer category. The Frenchman now has a 49.6s lead over Nikolay Gryazin's similar Fabia R5 heading into Saturday.
Leading times after SS11
|1||Jari-Matti Latvala, M.Anttila||Toyota Gazoo Racing WRT||Toyota||1h04m01.1s|
|2||Kris Meeke, S.Marshall||Toyota Gazoo Racing WRT||Toyota||1.2s|
|3||Esapekka Lappi, J.Ferm||Citroen Total WRT||Citroen||2.4s|
|4||Ott Tanak, M.Jarveoja||Toyota Gazoo Racing WRT||Toyota||2.6s|
|5||Craig Breen, P.Nagle||Hyundai Shell Mobis WRT||Hyundai||14.2s|
|6||Andreas Mikkelsen, A.Jager||Hyundai Shell Mobis WRT||Hyundai||14.6s|
|7||Sebastien Ogier, J.Ingrassia||Citroen Total WRT||Citroen||15.3s|
|8||Thierry Neuville, N.Gilsoul||Hyundai Shell Mobis WRT||Hyundai||30.9s|
|9||Teemu Suninen, J.Lehtinen||M-Sport Ford WRT||Ford||52.6s|
|10||Gus Greensmith, E.Edmondson||M-Sport Ford WRT||Ford||1m38.3s|
|11||Kalle Rovanpera, J.Halttunen||Skoda Motorsport||Skoda||3m08.6s|