Tokyo champion Alexander Zverev kept up his bid for a second straight Olympic men’s singles gold by winning 6-4, 7-5 on Tuesday against Tomas Machac – the Czech who beat him in the mixed doubles. Germany’s Zverev had teamed up with Laura Siegemund in the Paris mixed doubles but they lost 4-6, 5-7 to Czech Republic’s Katerina Siniakova and Machac on Monday. There was to be no repeat on Court Philippe-Chatrier at Roland Garros in the men’s second round as third seed Zverev easily took the first set. He grabbed the crucial break for 6-5 in the second with a forehand pass and served out a regulati…