Tanak completed the day's six demanding gravel stages with a 4.2s lead over Suninen, who impressed in only his third Rally1 start.
Tanak led the rally after winning the opening stage before losing the advantage following a spin and loss of hybrid in stage two. However, the 2019 world champion was able to rattle off two stage wins across the afternoon to regain the lead.
Toyota’s Elfyn Evans led the rally after the morning loop but the effects of his elevated road position dropped the Welshman to third, 12.7s adrift.
Hyundai’s Thierry Neuville recovered from handling struggles in the morning to snatch fourth (+27.7s) from championship leader Kalle Rovanpera, who was lucky to reach service only 38.7s behind.
Takamoto Katsuta held sixth in the third Toyota ahead of Rally1 rookie Gregoire Munster (M-Sport), while Hyundai’s Esapekka Lappi and M-Sport’s Pierre-Louis Loubet retired from the rally after rolls in stages one and three respectively.
After winning two of the three morning stages, Evans dropped from the rally lead to third after the afternoon’s first test, a second pass through Pulperia 19.77km.
Still feeling the effects of cleaning the road, Rovanpera's closest title challenger dropped 7.5s en route to setting a fifth fastest time that left him 4.9s adrift in the overall standings.
The lead initially swung towards Tanak, who posted a benchmark time, before Suninen delivered a blistering effort moments later to win the stage by 3.7s. The effort arrived after his Hyundai team elected to change the fuel tank on the Finn’s i20N during the midpoint service when a fuel pressure issue was detected.
The sister Hyundai driven by Neuville also showed an improvement in pace after fighting the handling of his i20N in the morning. The Belgian still wasn’t completely happy with his car, but managed to post the stage's third fastest time, 6.7s shy of Suninen.
"I think it's about the tyre management [of his one hard, three softs]," said Neuville. "I was managing the whole stage through, it's going to be a long afternoon. When I am managing the tyres I can drive the car, but as I push harder I go into a spin."
Rovanpera again faced the worst of the loose gravel road conditions and paid the price. He was the slowest of the Rally1 regulars, dropping 7.8s in the process.
As Neuville alluded, the afternoon developed into tyre strategy battle. Tanak elected for a package of six softs, which helped the Estonian win stage five (Rere, 13.34km).
Tanak responded to Suninen’s stage four effort to take the stage win by 2.5s from an improving Neuville. Running two hards and two softs, Suninen was third fastest, his time 4.9s adrift to drop 1.1s behind Tanak in the overall standings.
Loose gravel continued to hamper the early runners, with Evans reporting that he felt the stage was "more loose" than during the morning pass. He lost 5.1s but remained in third overall, 14.7s ahead of Rovanpera, who was 0.8s slower than his title rival.
The stage ran clean, although Katsuta was lucky to avoid a crash when he became crossed up following a jump that resulted in a brief run up an embankment.
Rally1 rookie Munster produced his best showing yet, now armed with his pacenote book after co-driver Louis Louka left his notes at the service park for the morning loop. Munster clocked the sixth fastest time, ahead of Katsuta, in stage five.
The day's final test was claimed by the soft tyre-shod Tanak, who extended his advantage over Suninen with a third stage win of the event to date. Tanak was 3.1s faster as Suninen managed a mysterious issue on his i20N.
Meanwhile there was a change on the leaderboard following a rare mistake from Rovanpera. The Finn ran wide, resulting in a brief off-road excursion that cost him 17.8s. This helped Neuville into fourth, despite him losing hybrid boost.
In WRC2, Sami Pajari led the class sitting in eighth overall ahead of Oliver Solberg, who survived the final 20 kilometres with damaged left rear suspension.
Six stages await the crews on Saturday.
