BUDAPEST (Reuters) -Ferrari feared Charles Leclerc might not finish Sunday's Hungarian Grand Prix after the Monegasque, who started on pole position, suffered a dramatic loss of performance after his second pitstop.

Leclerc pitted from the lead on lap 40 of 70 and ended up fourth, with teammate Lewis Hamilton 12th in a race won by McLaren's Lando Norris.

Team boss Fred Vasseur told reporters that the situation had been "quite strange" after being in control for the first 40 laps.

"The last stint was a disaster, very difficult to drive, the balance was not there. Honestly, we don’t know exactly what’s happened so far," he said.

"We have to investigate if there's something broken on the chassis side or whatever. At one stage I thought that we would never finish the race."

Leclerc had taken Ferrari's first proper pole of the Formula One season on Saturday, apart from Hamilton's sprint pole in Shanghai in March, and led cleanly away from the start at a circuit where overtaking is difficult.

Norris switched from a two-stop strategy to a one-stop, despite McLaren's initial reservations about the tyres lasting, after dropping to fifth on lap one and needing to do something different to teammate Oscar Piastri.

Championship leader Piastri had failed to get past Leclerc on strategy but was able to take second and close the gap to Norris after the Ferrari lost speed.

"We had to try and do something to beat Leclerc because it wasn't obvious that we just had enough pace to blow past him and go and win that way," said Piastri of a failed attempt to get ahead with an earlier first pitstop.

"I don't know what happened to Charles in the second half of the race, but clearly something happened because he looked quite quick for the first half."

(Reporting by Alan Baldwin, editing by Pritha Sarkar)