The 40-year-old opened up a sizeable 34.6sec advantage with his Škoda Fabia Rally2 Evo on a day when conditions and grip levels were changing by the kilometre.
Kopecký, who set the pace on Friday evening’s city-centre super special, was hampered by a poor tyre choice in the opening test. He left the morning service with four medium compound Pirelli slicks bolted to the car and, just as he was about to start the stage, the heavens opened.
Dropping 9.7sec to Adam Brezík’s Fabia, which was equipped with wet weather tyres, the nine-time Barum winner slipped from first to third overall. Luckily for Kopecký, however, the setback was short-lived.
A monumental charge on the very next Držková blast launched the local ace back in front as he stopped the clock 18.4sec quicker than anybody else. That earned Kopecký ample breathing space, although he was in no mood to compromise.
Three more well-worked benchmark times vaulted him even further clear of the field and he remains on track for a 10th win in Zlín with one day remaining.
"For sure, we are trying to control our pace a little bit because we don't want to make any stupid mistakes," said Kopecký.
"In the second pass there were some sections where the grip was even worse than in the morning. In some places I was understeering in third and fourth gear," he added.
Erik Cais was Kopecký’s nearest challenger as well as the only non-Škoda driver in the top five with his Ford Fiesta Rally2. The 23-year-old had a shaky start but, after making some set-up tweaks in service, he found the confidence to win the second pass of Držková.
Filip Mareš filled the final podium spot 13.6sec behind Cais despite a turbulent morning. He spun once and ran wide another two times, clipping a rock which left his Entry Engineering team with plenty of work to do at the mid-leg halt.
Just 9.5sec further back was Simon Wagner. Running slick tyres in waterlogged conditions, the Austrian also suffered a spin and lacked confidence at times.
Nevertheless, Wagner headed fifth-placed Norbert Herczig by more than two minutes, with Herczig’s Team MRF Tyres Škoda colleague Simone Campedelli another 6.0sec in arrears.
An anxious Alberto Battistolli resigned himself to simply tip-toeing through the punishing asphalt stages but still ended the day seventh overall ahead of Albert von Thurn and Taxis and Martin László’s similar Fabia cars. Martin Vlček completed the leaderboard almost five minutes adrift of the frontrunners in a Hyundai i20 R5.
Brezík ended over seven minutes off the pace after a turbo pipe worked itself loose at Brezová and Javier Pardo also haemorrhaged time when he stopped to change a wheel mid-stage.
Sunday’s finale features two loops of three tests totalling 95.88km. Up first are Bunč (15.20km) and Maják (13.20km), followed by a run through Pindula (19.54km) - a true Czech classic.
Newly-crowned FIA ERC champion Efrén Llarena crashed his Škoda into retirement on SS2. He and co-driver Sara Fernández emerged from the wreckage unassisted but were taken to hospital for precautionary checks.
Tom Kristensson also failed to finish after the Swede slid his i20 into a tree on the same stage, while Estonia's Ken Torn rolled his Fiesta on SS3.
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