Oscar Piastri suffered his worst qualifying session of the year at the Mexico City Grand Prix on Saturday. Piastri had maintained a 100% Q3 record through the first 19 races. The Australian looked like a contender for pole position after topping FP3 on Saturday morning. But an error-strewn Q1 led to a major upset. Piastri found himself under pressure after locking up at turn four. He later lost a lap time for exceeding track limits at turn 12, just before the stadium section. The 23-year-old hadn’t qualified lower than fifth for a Grand Prix since Austria. But he did tarnish his stat sheet in …