Sainz controversially benefitted from being allowed to take his original third place on the grid for the Monaco restart after its early red flag, with Zhou’s role central to how things played out.
The Ferrari driver's race had initially appeared to be over just a few seconds after the start when the Spaniard picked up a puncture as he clashed with Oscar Piastri at the first corner.
A small cut in his front left tyre, likely from Piastri’s floor, was enough for his tyre to lose air pressure and leave him a passenger as he skidded wide at Casino Square.
As he initially came to a halt, the rest of the pack came streaming past and left him facing up to a potential non-points score as he moved to find reverse and trudge slowly back to the pits.
But his afternoon turned on its head when, just as he reached the hairpin – with the leaders already on their way out of the chicane – the red flag came out because of the crash involving Sergio Perez and the two Haas cars.
In ordinary circumstances, the red flag would not have been of tremendous benefit to Sainz beyond meaning he would not end up completely adrift of the pack for the subsequent restart.
He almost certainly would have been shocked to have been told that he would not be taking it from the 16th place he was on the road.
That is because F1’s sporting regulations are clear in how they take the order for any restart from a red flag.
They state that: “It will be taken at the last point at which it was possible to determine the position of all cars.”
From the outside, it was fairly obvious from the television images where the cars were running when the red flag came out, but that is not good enough for determining the grid.
Instead, as was highlighted amid a similar red flag situation at the 2023 Australian Grand Prix when Haas was upset that Nico Hulkenberg had been moved back at a red flag restart despite being fourth on the road at the time, the FIA has precedent for taking the quickest and more reliable route it can.
Using GPS data is not good enough for being totally sure about the positioning of cars relative to each other.
As was stated by the stewards in the 2023 Australian GP verdict: "They [Haas] acknowledged that the GPS data that showed the relative positions of the cars was unreliable for the purpose of establishing the order of cars."
So just as in Melbourne, the FIA had to go back to a point where it had complete timing data for all the cars.
It is understood that race control had initially looked like being able to use the first sector timing line that is situated at the entrance to Mirabeau for this.
However, this did not prove possible because not all the cars that were still running had crossed the line by the time the red flag came out and the fact that Sauber’s Zhou, after a poor getaway from the grid, had lost a lot of time being delayed behind the Perez crash was crucial.
First, he had tried to avoid being caught up in the chaos, but then he also waited to find a clear path through the wreckage with the medical car stationary on track. When the red flag came out, he was only at the entrance to Massenet.
So, with the FIA unable to use the S1 timing line as its marker for deciding the grid, it had to use the most reliable previous reference point – which is safety car line two (SC2).
In Monaco, this is on the exit of the first turn and is a white line that signifies the point on the track where the pit lane exit line ends.
With all cars having crossed this line at the point the red flag came out, this became the reference order for the restart.
This meant that Sainz would take the third place that he was running in when he crossed SC2, with a couple of drivers being shuffled around based on how they had done out of the first corner.
Watch: F1 2024 Monaco GP Review – Leclerc Finally Breaks the Curse
For example, Lance Stroll had got himself ahead of Daniel Ricciardo for 12th, with Zhou taking the 17th and final spot thanks to Perez and the two Haas being non-starters.
While Lando Norris in particular felt that it was “unfair” that Sainz had got his third place back after what had happened to him, his team boss Andrea Stella accepted that how the FIA applied things for the restart was correct – and Zhou had been a key player in what happened.
“I think what the FIA did was the best thing to do,” he said. “Also, it is in agreement with the precedent, whereby you use the safety car line 2 when a sector time is not available.
“I don't think using the mini sectors is a good way of doing that. And obviously, the whole point that saved Carlos was that Zhou had not crossed the sector time at the time the race was suspended. Lucky Carlos…”
