The 2019 world champion dialled back his pace in a bid to preserve his advantage on the final morning, but the Estonian increased his lead over M-Sport’s Craig Breen to 56.9s.
Hyundai’s Dani Sordo consolidated third spot with a 36.4s margin over M-Sport’s Pierre-Louis Loubet, who is on course for a career-best WRC finish.
Championship leader Kalle Rovanpera ended the morning loop in fifth overall, 2m55.0s adrift of the lead having struggled opening the rough gravel roads on Friday.
Rovanpera’s Toyota team-mate Takamoto Katsuta and M-Sport’s Gus Greensmith completed the Rally1 field.
Despite backing off his speed, Tanak claimed his eighth stage win of the event by claiming the opening test of the day.
Tanak completed the pass 1.7s faster than the returning Toyota of Esapekka Lappi, after the Finn crashed out of the lead on Saturday.
Breen was third fastest, letting slip more time to Tanak, but the Irishman was fully focused on ending the rally in second to equal his career-best WRC finish.
"I'm only driving at five or six tenths," said Breen. "I would dearly love to be on the podium today, so that's the plan."
Sordo was also in a similar mindset, as the Spaniard clocked the fourth-fastest time.
Toyota’s Elfyn Evans and Hyundai’s Thierry Neuville rejoined the rally after retirements on Saturday, but the pair cruised through Stage 18 to preserve their tyres for the rally-ending powerstage.
The pair did spark into life on Stage 19, the first pass through Sassari, that will act as the powerstage this afternoon. Neuville took the stage win by 2.4s from Evans with Lappi in third.
Tanak was fifth fastest but wasn’t in the mood to take any risks, revealing that he has taken two of the more durable hard tyres as an extra precaution.
"I took two hard tyres in the car because we need to bring it to the finish and minimise the risk of punctures basically," said Tanak. "The car is working okay, but this one is going to be very rough later."
Rovanpera elected to save his tyres during the test, but wasn’t confident he will figure in the powerstage later today.
"It was okay," he said. "I am trying to save the tyres a bit.
"It would have been better to go fast and feel it for the next pass, but I think the powerstage will be so rough that it won't make a difference."
The crews will repeat the two morning stages to conclude Rally Sardinia this afternoon.
