De Vries lays down a marker on dream debut in F1 with Williams
The Dutchman started eighth, as penalties moved others down the field, and finished ninth in the Italian Grand Prix at Monza to score two world championship points.
He could have done little more to boost his prospects of securing a full-time drive next season.
The man he might replace, Canadian teammate Nicholas Latifi (27), finished an underwhelming 15th after starting 10th and remains the only driver on the starting grid yet to score a point from 16 races.
"This has been incredible. Points on debut," de Vries said over the team radio, complaining also that his shoulders were 'dead'.
"Great job, Nyck. Fantastic. You so much deserve it," team principal Jost Capito told him.
The Mercedes reserve was summoned on Saturday morning, just as he was preparing for a weekend of hospitality duties with guests, after Williams regular Alex Albon (26) went down with appendicitis.
Ninth place equalled Albon's best result this season.
De Vries seized his chance and out-performed Latifi despite the short notice and the fact he had driven a completely different car, the Aston Martin, in first Friday practice.
He had also not driven the Mercedes-powered Williams on a full fuel load before.
"Driver of the day makes me so happy and I'm very pleased and thankful that I got given the opportunity and I grabbed it with both hands," he said.
"Hopefully I will get a shot next year, but this is definitely a dream come true and I'm very impressed with what we've done in short notice, so I'll go enjoy it now."
The 2019 Formula Two and 2021 Formula E champion said he had a rough night.
"The whole of the last 24 hours has just been a dream," he said. "Basically I spent the whole night awake but perhaps it helped me.
"I couldn't think and I just had to get on with the job."