Rovanpera set a blistering pace across the day’s six stages aboard his factory Toyota to lead team-mate Elfyn Evans by 56.9s heading into Saturday.
Takamoto Katsuta ended the day in third [+1m00.8s] to set up a provisional Toyota 1-2-3 after a nightmare day for Hyundai.
Lappi had trailed Rovanpera by 15.5s heading into the afternoon before a transmission issue ended the Rally Sweden winner’s day prematurely. That handed Tanak second spot before the Estonian crashed out on the following stage.
Championship leader Thierry Neuville, piloting the remaining Hyundai, survived a puncture on stage three to complete Friday in fourth [+1m07.3s], in front of the M-Sport-Ford duo Adrien Fourmaux [1m46.6s] and Gregoire Munster [+3m34.2s].
Conditions remained hot into Friday afternoon, but the clear skies were replaced by ominous grey clouds.
Rovanpera continued his impressive pace from the morning loop by claiming his fourth consecutive stage win in the second pass through the Loldia [19.17km] test.
The Finn was still not overly happy with his effort but was able to pip Toyota team-mates Evans and Katsuta, who posted identical times, to win the stage by 0.6s. Both Evans and Katsuta were much happier with the handling of their GR Yaris entries.
This meant Rovanpera was able to extend his overall rally lead, although the identity of his nearest rival had changed.
Lappi started stage five trailing Rovanpera by 15.5s but his hopes of victory were quickly extinguished. The Finn suffered a small impact nine kilometres into the rough gravel stage which damaged his transmission, forcing him onto the sidelines.
Lappi’s Hyundai team-mate Tanak jumped into second overall, 18.6s behind leader Rovanpera. Tanak was 1.8s slower than Rovanpera in the test but revealed that his team had been unable to work on his car in service due to the extent of the damage on team-mate Neuville’s i20 N, following his puncture this morning.
«[Lappi out,] that is a shame, big shame. For us, a difficult stage once again,” said Tanak. “Thierry’s car took so much work that they couldn’t work on our car. Let’s see if we can work on it ourselves.»
Thankful his team was able to repair his car, Neuville was fifth fastest on the stage behind Fourmaux, who showed the first flashes of strong pace in his M-Sport Ford Puma.
However, Hyundai’s Safari Rally hoodoo struck again in stage six [Geothermal, 13.12km], this time it was Tanak to hit terminal trouble.
The 2019 world champion hit a rock sitting in the middle of the road which launched the front of his i20N into the air, before coming to blows with an earth bank. While Tanak and co-driver Martin Jarveoja were unhurt, the impact damaged the steering of their Hyundai that had been occupying second position.
Tanak’s demise handed Rovanpera a healthy 46.4s lead after the Finn’s 100% Friday stage-winning streak continued. Rovanpera was 4.5s quicker than team-mate Katsuta through the rocky stage, while Evans was a further three seconds slower.
Munster made the most of cleaner road to post the fourth best time ahead of Fourmaux and Neuville. The latter was lucky to survive a big moment that could easily have sent the Hyundai into a ditch.
Rain fell before the start of the final stage, but conditions were reasonably dry by the time the crews tackled the 31.50km Kedong test.
Rovanpera once again proved to be the class of the field, posting a time 4.4s faster than road opener Neuville to complete a clean sweep of the day’s stages.
Evans managed to leapfrog Katsuta into second overall after the latter missed a junction that contributed to him ceding 8.7s to his rival.
In WRC2, Toksport Skoda driver Gus Greensmith battled a stomach bug to end the day in seventh overall [+6m51.3s]. The British driver held a 3m23.0s lead over nearest WRC2 rival Kejetan Kajetanowicz.
The Safari Rally continues on Saturday with the field set to tackle the longest leg of the event, comprising 160.96 kilometres of timed stages.
Watch: Safari Rally Kenya Friday Morning Highlights