Saina, the London Olympics bronze medallist, defeated eighth-seed South Korea's An Se Young 25-23, 21-12 in a match that lasted for 39 minutes.
Reigning world champion Sindhu, seeded sixth, took just 35 minutes to beat Evgeniya Kosetskaya of Russia 21-15 21-13 in the first round
India also won nine medals, including two golds, in taekwondo and one gold, two silver and a bronze in the triathlon event on the opening day
Shubhanker Dey now remains the lone Indian in the men's singles contest, having progressed to the second round where he will be up against Shesar Hiren Rhustavito of Indonesia.
While Sindhu and Okuhara battled for 110 minutes during the 2017 World Championships final match, the duration of Sunday's match was just 38 minute
With three or four genuinely world-class players, badminton has established itself as India's boom sport
A semifinal finish at Lucknow also saw Mumbai's Harsheel Dani's rank jump to 69
Olympic silver medallist P V Sindhu entered the top 10 but Saina Nehwal crashed out of the elite bracket
The BWF International series is slated to take place at Islamabad from October 18-21
Nehwal will next take on the winner of the match between fourth seed Wang Yihan and eighth seed Tai Tzu Ying