Team chief Toto Wolff praised George Russell and compared him to "a finance guy" because of his serious nature on Saturday after the young Briton qualified second for Sunday's Sakhir Grand Prix.
The 22-year-old Williams driver, loaned to Mercedes this weekend to substitute for coronavirus victim and seven-time champion Lewis Hamilton, was only 0.026 seconds slower than Mercedes team-mate and pole-man Valtteri Bottas.
"I said to him 'if you end up in the first four, that's great and if you get passed by someone and up in fifth, that's fine too,'" said Wolff. "But that's already a fantastic result today.
"Nothing more is expected so we will go with a little bit more easiness. I think he settled in well and, considering the track is new for everybody, I'm happy with his performance."
Speaking to Sky Sports F1, Wolff added that Russell had injected a different atmosphere into the Mercedes garage.
"They're so different characters," he said. "Lewis has been there for a long time and he is quite quiet. George is a lot more chatty – and he is quite serious.
"You would think he was a finance guy! He settled in well, even though he doesn't really fit into the car."
Russell admitted he felt bruised and battered after squeezing his taller frame and bigger feet into a cockpit tailored for fellow Englishman Hamilton who the team hope to see recovered from Covid-19 in time for the season-ending race at Abu Dhabi next weekend.
"We've given him a lot of support and extra time," said Wolff.
"It's very difficult for a racing driver to see someone else in the race car. I haven't asked him how he felt today, but if he tests negative (next week), then we can expect him in the car in Abu Dhabi."