The 22-year-old from Hyderabad, who had won her maiden Denmark Open title last Sunday, looked in control throughout the second round match against Sapsiree and prevailed 21-16 21-13 in a 37-minute women's singles event to move into the quarterfinals.
The top seeded Indian rode on her eight smash winners and 12 clear winners to claim her second victory over world number 27 Sapsiree. Saina had beaten her in the All England Championship in March this year.
Saina, who jumped one place to reach the third spot in the latest world badminton ranking today, initially engaged in a fierce battle with the Thai girl, before opening up a narrow four-point lead midway at 12-8.
Sapsiree clawed back at 13-13 but Saina soon reeled off five straight points to extend the gap, which the Thai girl failed to bridge.
In the second game, Saina didn't allow Sapsiree any chance to cut down the lead as she dominated right from the start. From 4-1, the Indian consistently surged ahead.
Saina is likely to take on another Thai girl in seventh seed Ratchanok Intanon, who will face Indonesia's Aprilla Yuswandari in another pre-quarterfinal match.
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Intanon, who won the World Junior Champion for three consecutive years in 2009, 2010 and 2011, is one of the fastest rising shuttlers in world badminton.
The world number 10 Thai holds a 1-3 record against Saina. She had beaten the Indian once in 2011 Sudirman Cup.