The race for the overall win took a fresh twist in the 19th hour when the leading #51 Ferrari 499P failed to get away immediately after its pitstop as Antonio Giovinazzi handed over to Alessandro Pier Guidi, requiring a power cycle to get going again.
That eradicated an advantage of a minute that Ferrari had over the sole surviving Toyota GR010 Hybrid, the #8 car, which had been bolstered by slow zones that hurt the car driven by Sebastien Buemi.
After that, Buemi closed right in on Pier Guidi, even getting within a second of the Ferrari man at one stage, before the Italian opened the advantage up again.
Buemi handed over to Brendon Hartley at the next round of stops, costing the Toyota ground as Pier Guidi stayed on board the Ferrari, with the two cars then circulating around 20 seconds apart.
However, Toyota mixed up its strategy by bringing in Hartley earlier than the pit schedule that he and Pier Guidi had been running on, sending out the Kiwi with fuel only.
Ferrari reacted by bringing in Pier Guidi the following lap, with James Calado taking over at the wheel and coming under pressure from Hartley as he headed back out on circuit.
The gap between the two leaders shrunk to as little as 1.4 seconds with four hours to go before Calado started to stretch his legs at the head of the field again, and the 21-hour mark, Calado was 14 seconds ahead of Hartley.
The third-placed #2 Cadillac V-Series.R, the only one of the American marque's cars to have enjoyed a clean run up to now, dropped off the lead lap in the 20th hour.
Source: Autosport