World No. 1 Saina continued her rampaging run in world badminton and staved off a challenge from Sun, ranked 9th, 21-19 19-21 21-14 in a match that lasted an hour and 18 minutes in the women's singles competition.
The Olympic bronze medallist will next take on two-time All England champion Shixian Wang, against whom Saina has a close 6-5 record in 11 meetings.
However, it was curtains for World No. 4 Kidambi Srikanth and 2010 Commonwealth Games champion pair of Jwala Gutta and Ashwini Ponnappa today.
Saina, who had beaten Sun thrice in the last four meetings, came out with a well-thought strategy as she broke off at 5-5 and entered the interval with a 11-6 lead.
Also Read
Sun played better after the interval to slowly narrow the gap before clawing back at 18-18, but a determined Saina zoomed ahead to pocket the opening game.
An alert Saina held her nerves and moved to 18-15 but she could not stop a fighting Sun, who roared back into the contest with a three-point burst from 18-19 behind.
In the decider, Saina didn't allow Sun to threaten her in anyway as she led from the start and at one stage was comfortably placed at 12-4.
Though the Chinese tried to erase the deficit, Saina made sure there was no more hiccups and eventually sealed the issue in her favour.