What happened: Russell was running third under the safety car at Sepang when the power unit failed at Turn 1 with five laps remaining. Mercedes said exceeding the four-unit seasonal allowance sends him to the back at Marina Bay, where he won last year.

Why it matters: The penalty stalls his chase of teammate Kimi Antonelli, who leads by 84 points with seven rounds left. It shifts Mercedes' winning burden to Antonelli after Max Verstappen controlled Sepang from pole with Antonelli second.

What to watch: Mercedes will split latest and previous update packages across Singapore practice to clarify its direction. Sunday focus becomes Russell's recovery drive and Antonelli's title lead.