The pair came together as Sainz attempted to slither up the inside into Sainte Devote on the opening lap, understeering into Piastri as they exited the corner.
The Ferrari’s left-front wheel make contact with the sidepod and floor of the McLaren, leaving Sainz with a puncture that looked set to end his race just metres later.
However, a sizeable crash between Sergio Perez and the two Haas drivers drew an opening lap red flag, allowing Sainz to limp his car back to the pits where he was restored to third for the restart.
“I got a really good start and then I had kind of an opportunity coming into Turn 1,” Sainz explained.
“I arrived a bit long, with a lot of understeer in the car.
“We had the slightest of contacts. For some reason, Oscar and I, we seem to have a magnet recently.”
The contact cut Sainz’s front tyre but did no other damage, while for Piastri it was rather more significant.
“I definitely felt the touch at Turn 1,” he said when asked about the clash by Speedcafe.
“That part of the car, it’s such a sensitive part.
“The team told me how much downforce I was losing before we tried to fix it, and it was a pretty big number.
“I don’t know what we managed to get it down to, but obviously, the length of the red flag helped us out quite a lot.”
McLaren replaced the right-hand sidepod on Piastri’s car under the stoppage and did what it could to repair the damaged floor.
“Being in Monaco, probably the one track where having damage doesn’t hurt you as much,” Piastri noted.
“It was a very, vert small touch, but with the cars, especially with the floor, it’s so sensitive to the downforce it generations, it can ruin your race very easily.”
When the race resumed, Piastri maintained second, shadowing leader Charles Leclerc for much of the race.
The Australian even attempted a move in the early laps before the extent of the damage on his car began to tell.
“I had an attempt about 10 or 15 laps in at Turn 8,” he recounted.
“We were going pretty slow. I think at one point we were going slower than Formula 2!
“When you’re going that slow, you’ve got a fair few options, but I kind of knew that once I showed my hand in where I was going to try and overtake, that he would probably be wise to it.
“I managed to get very close at Turn 7 one lap, tried to show the nose at Turn 8, but he reacted just quick enough.”
With the door closed, Piastri fell back in line behind the leading Ferrari, remaining in contact until the close stages when Leclerc increased the pace.
The McLaren driver could not go with him as the effects of his Lap 1 clash with Sainz began to have an impact.
Instead, spend the closing laps defending his second position, thankful for the narrow confines of the Monaco streets.
“For the first half of the race, it was impossible to tell what the penalty of that was,” Piastri said of his Turn 1 damage.
“Towards the end, I think probably a combination of trying to keep the pace reasonably quick, plus the floor… just struggled a bit towards the end.
“The last 10 laps or so, I was pretty happy we were in Monaco [where overtaking is difficult].
Piastri crossed the line 7.1s back from the race winner Leclerc, who slowed on approach to the flag, with Sainz just four-tenths back in third. It marked the 23-year-old’s first podium of 2024 and the third of his career.