Once the race had settled into a predictable rhythm, and the two Ferraris had opened a comfortable advantage over third placed Hamilton, Leclerc was told over the radio that Vettel would let him through on the next lap.
“Sebastian will let you by next lap,” came to call to Leclerc.
However, Vettel was unwilling to wave his team-mate by.
“I would have got him anyways, but let's breakaway for another 10 laps, let me know,” came the German's response.
“Then tell him to close up,” he argued when again instructed to allow Leclerc through.
As the situation developed an aggrieved Leclerc began to vent his frustrations.
“You put me behind,” he stated.
“I respected everything. We'll speak later but now is not good to close the gap, obviously.”
Ultimately the team was forced to play the strategy card, using the undercut to bring Leclerc in three laps earlier than Vettel.
That saw the pole-sitter reclaim the track position he'd lost at the start, but left Vettel vulnerable to Hamilton.
However, that would prove a moot point as the German retired little more than half a lap later with MGU-K failure.
“The tactic was me giving the slipstream, to be one-two at the end of the straight, which happened but then I don't know, I need to speak with the team,” said Leclerc when asked of the arrangement post-race.
For his part, Vettel remained coy, refusing to be drawn into any finger pointing.
“We had an agreement,” he confirmed.
“I spoke with Charles in particular before the race, I think it was quite clear but I don't know, maybe I missed something.
“I'm sure we will talk about it but obviously bitter today because we wanted to have one and two.
“I don't want to share, to be honest,” the German added when pressed for further detail on the agreement.
“I just don't want to put the team in a bad position afterwards because somebody said something here and there.
“I know it's not fair because I think people deserve to know, it's not a big deal.
“I was in third, Charles was in first, we were talking about a strategy to find a way past Lewis.
“Obviously I had a very good start so there were a couple of options on the table.”
Team boss Mattia Binotto was more forthcoming, confirming the intent was to use Leclerc's slipstream to move Vettel clear of Hamilton, and then restore Leclerc to the race lead once they were clear of the Mercedes.
“What was the deal? Simply the deal is Charles would have given the slipstream at the start to Seb to make sure that we would have been first and second at the first lap, as that would have put us in the best position to control and manage the race – which was the case up to the point of the unreliability,” Binotto told Sky Sports F1.
“But Seb was very fast, in the race, so I think the decision could have been postponed.
“Initially we asked him to swap, that was not the case because Charles was not sufficiently close to him, and that was the deal. That was all.”
Leclerc's race unravelled further courtesy of an MGU-K failure for Vettel, which saw the German stop out on track.
With the Virtual Safety Car deployed, Mercedes gained a cheap pit stop, allowing Hamilton to rejoin the race ahead.
He ultimately trailed home behind both Mercedes drivers, who claimed a surprise one-two result.