Pascal Wehrlein said he had no idea where the Williams-matching pace behind his first Formula 1 points for Manor in the Austrian Grand Prix came from.
Wehrlein was chasing Valtteri Bottas's Williams for 10th going into the final lap, when a brake-induced crash for Sergio Perez elevated both a place.
It gave Manor only the second points finish of its F1 history, and the first since Jules Bianchi's Monaco 2014 ninth place when the team was running as Marussia.
Wehrlein had qualified 12th, but fell to the back when he pitted just before the safety car for Sebastian Vettel's tyre failure.
He then made his soft tyres last 48 laps as he hunted down Bottas, who was on super-softs fitted 28 laps later.
"I thought 'the race is done' because we were so unlucky with the safety car," Wehrlein admitted.
"But I kept pushing and trying to manage my tyres because I didn't want to stop again.
"I was hoping to get a crazy scenario when [Nico] Rosberg and [Lewis] Hamilton were coming in the blue flags and have an advantage because of that.
"Otherwise it would have been difficult to overtake [Bottas] because he was on 10 or 15 lap old super-softs and I was on more than 40 laps old soft tyres.
"I was still able to fight with him so it was a great performance today from the car and I don't know where it was coming from."
Team principal Dave Ryan reckoned Wehrlein would have passed Bottas and got ninth had the leaders not disrupted their battle.
"We thought we'd get him quite easily, if it hadn't been for the leaders coming through," Ryan told Autosport.
"That kind of upset the rhythm for two laps.
"But he was shaping up to have him and we could have had him."
Wehrlein reckoned Manor's Austria upsurge was largely due to it getting the tyres to work better at the Red Bull Ring.
"It's the first weekend that we are not struggling with tyre temperature," he said.
"We don't have so much downforce as the other teams and downforce puts a lot of energy into the tyres.
"It's the first weekend we are even overheating the tyres. We haven't had this before and it helped us a lot."
He also admitted he was fortunate not to be penalised for initially lining up in pitlane starter Felipe Massa's vacant 10th-place grid slot, before reversing into his own place.
Wehrlein was able to complete his move and line up correctly before the lights started coming on for the start process.
"I reversed, stopped, put it into first gear then I saw the first light come," Wehrlein said.
"Half a second later I'm sure that was it [a penalty].
"Then you have so many buttons to put the engine mode in and another thing to put in, then I needed to find the reverse gear and I was like a DJ on my steering wheel."