TOKYO—Mixed-race Japanese tennis star Naomi Osaka on Friday lit the Olympic cauldron to mark the formal start of Tokyo 2020, in an opening ceremony shorn of glitz and overshadowed by a pandemic but celebrated as a moment of global hope. Organizers also paid tribute to medical workers as athletes from across the world paraded into an almost empty stadium, their smiles hidden behind masks for the first time. Normally a star-studded display teeming with celebrities, the ceremony was low-key, with fewer than 1,000 people in attendance, strict social distancing rules, and signs calling on spectators to “be quiet around the venue.” “With the world in a tough situation because of the coronavirus pandemic, I would like to pay my respect and express my gratitude to medical workers and all those who are working hard every day to overcome the difficulties,” said the President of the organizing committee, Seiko Hashimoto. The …