BUDAPEST, Hungary — Oscar Piastri was left fuming with Carlos Williams' Sainz for showing an "unacceptable" lack of awareness after a collision while lapping the Williams driver cost him the chance to fight for victory in the Hungarian Grand Prix.

Piastri had been in contention for victory at the foot of the Hungaroring on Sunday, leading the opening stint of the race from McLaren teammate Lando Norris. But Piastri's hopes of a first win of the year were all but ended after his second pit stop when he made contact with Sainz at Turn 2 while trying to lap the Williams driver, who was battling Fernando Alonso at the time for 16th place.

Sainz later received a five-second time penalty from the stewards for causing a collision. Under F1 regulations, drivers being lapped are required to allow those on the lead lap to pass to ensure they do not have a negative impact on their races.

It emerged after the race that there was an issue with the automated blue flags system that normally notifies drivers they are about to be lapped with blue flashing lights both on the panels at the side of the track and on their steering wheels. Race control instead relied on marshals waving flags and pressing the button for the light panels to notify drivers.

After the collision — which caused Piastri to momentarily lose total control of his car and drop a couple of seconds — Norris was able to emerge from the pits just ahead of the Australian. While Norris pulled away and went on to win the race, Piastri eventually retired with 15 laps to go due to a gearbox failure.

Piastri told Sainz to "get out of the f—ing way you make" over the radio following the clash, and asked if he was "f—ing stupid or what." He remained unimpressed with the Spaniard when speaking to reporters in the media pen afterwards.

"I knew there were blue flags, but there were blue flags on all the rescue signals, I was right behind him for a sector," Piastri explained. "I couldn't believe what happened. Getting crashed into by a lapped car is never one of the things you expect can go wrong in your race, and today it was."

"The fact that he didn't and no one told him, or there was a lack of complete awareness, is unacceptable."

Sainz, however, explained that the blue flag system issue meant he did not have the usual blue lights on his dashboard that would typically have helped while he was focused on the battle with Alonso.

"I had no idea I was about to get lapped, and on top of that, I was in a bigger fight with Fernando trying to u-carry him into the corner," said Sainz. "I wouldn't have expected Oscar to be there, and even if he was there, or maybe he was on my death spot on the angle, so it was impossible honestly from my side to avoid it. Probably a better communication would have helped, but at the same time (it was) a racing thing."

Sainz added that while he felt sorry for Piastri, he thought he had "a pretty good excuse for what happened," saying he would expect the McLaren driver could have been "a bit more careful, given that he's the one fighting for podiums." Piastri took a dim view of that defence, saying the Williams driver was fighting Alonso "like it was (for) the world championship."

"He's quite critical of others and others have given him some stick before for being too aggressive on-track," Piastri said. "When you go and do something like that, maybe you should look in the mirror a bit."

After Norris emerged from the pits in the lead, Piastri appeared to question McLaren's strategy decision, but he clarified later that his frustration was directed at Sainz rather than the team.

"We wanted to cover off (Lewis) Hamilton, which was perfectly normal," Piastri explained. "Without getting crashed into, I would have been ahead of Lando still. So that side of things I was fine. In the moment I was incredibly annoyed — in fact annoyed is not the word I would use, there's a multitude of that — with Carlos. Then obviously when Lando came out ahead, I knew I had no pace to go and attack him. I knew my chances of winning the race were done from there."

"So in the moment, yeah, I was pissed off that I'd lost the lead of the race, but that wasn't the fault of the team, it was Carlos's fault."