Becomes only third Indian to win a singles match at the Games.
Sumit Nagal became only the third Indian to win a men's singles match at an Olympics and the first in 25 years, when he edged past Denis Istomin in a three-setter at the Tokyo Games on Saturday.
Nagal got the better of Istomin 6-4, 6-7(6), 6-4 in two hours and 34 minutes on court 10 at the Ariake Tennis Centre to set up a second round with World No 2 Daniil Medvedev.
Zeeshan Ali was the first Indian to win a singles match at the 1988 Seoul Games when he beat Victo Caballero from Paraguay.
After that, the legendary Leander Paes won the historic men's singles bronze at the 1996 Atlanta Games, beating Brazil's Fernando Meligeni.
No Indian has won a singles match after Paes's heroic feat even as Somdev Devvarman and Vishnu Vardhan competed at the 2012 Games in London but did not manage to move past the first round.
The 23-year-old Nagal, who did not come into the Games in his best form, had a break opportunity in the sixth game of the opening set but could not convert.
The Indian, though, did not squander the opportunity when Istomin was serving to stay in the set.
An early break pushed Nagal ahead 2-0 in the second set in which he raced to a 4-1 lead but nerves got the better of him when he was serving for the match, up 5-3, and he dropped his serve.
The experienced Istomin forced a decider by prevailing in the tie-breaker.
The final set was on serve till Nagal got the decisive break.
Nagal now faces a herculean task as he faces Australian Open runner-up Medvedev, who beat Kazakhstan's Alexander Bubilk 6-4, 7-6(8).