The pair came together on the opening lap of Sunday's Spa race, with Sainz, who started fourth, locking up and colliding with Piastri on the inside of Turn 1.
The McLaren was pinched against the inside wall, damaging its suspension and ripping the side of the Ferrari’s right sidepod, with Piastri slowing on the run downhill to Eau Rouge and later stopping.
Though the stewards took no action over the incident, Sainz said he felt the rookie should have yielded, especially given Sainz was mid-fight with Mercedes driver Lewis Hamilton.
He said: “He attacked with Lewis and I pretty much had the move done into Turn 1.
“Hit the apex cleanly and everything but unfortunately I think Oscar was trying to do a bit of an optimistic move on me.
"Yeah, a bit of a shame because when you review the past races here in Spa and you know what has been the typical Turn 1 incidents, it’s exactly that.
“Everyone who tries the inside line into Turn 1 and tries to really make around there normally generates an incident or a crash and this time it was my turn to receive.”
Sainz insisted he did not go deep at the corner, though he accepted he locked up, and said he “made perfectly the apex and passed Lewis.”
He said he knew Piastri was on the inside, but added: “At some point someone needs to back out and he’s the guy who is alongside my rear-right that I think needs to back off and move, not me, and let him pass me into Turn 1, especially when I’m pretty much having my move done with Lewis.”
Sainz said the car was “undriveable pretty much” but continued in case of a red flag before retiring once the rain had passed.
Piastri said he felt the incident was “quite firmly in the category of a lap one, Turn 1 incident” but said it was “a shame” after his sprint race podium on Saturday, finishing second behind Max Verstappen.
Explaining the incident, he said: “I got a good start and got my nose alongside, and then when we got to the braking zone Carlos moved a bit to the right and locked up and I also had to try and avoid that a bit.
“From there to the apex, my options were quite limited on where I could go.
“I’ll look back over it and see if there was more I could have done but yeah, just a shame that we’re standing here and not still on track.”
Piastri said he felt both drivers “could have done things a bit differently,” but added: “It’s a very tight Turn 1, Carlos also didn’t have many options from where Lewis was either, so it’s a shame.”
He told Motorsport.com: “I think from Carlos’s point of view, the move to the right surprised me a bit.
“Then for myself, I think from there I was quite limited, maybe I could have braked a bit later and been further alongside, but it’s very easy to say that with hindsight.
“I think once I was in that position it was quite hard to either go forward or go backwards, and I was kind of stuck.
“I tried to do the best I could from that position but there wasn’t much I could do.”
The Australian said he had suffered a front puncture and broken steering in the crash, forcing him to drive up Eau Rouge “with about 180-degrees of lock and still going straight.”
