In a tense final set, World No.533 Diatchenko twice served to stay in the match before ultimately prevailing, 6-3, 2-6, 7-6(3).
Making a mockery of her lowly ranking, the Russian withstood a final set fightback - and 15 aces - from Broady to register only her sixth win of the season.
"I have such nice memories from two years ago," Diatchenko said. "The season was not the best because I had surgery on my Achilles and I could not play all the season. I felt like I was only really playing tournaments pain-free after the US Open. But after this match I can start to feel more confident because I beat a Top 100 player."
Diatchenko, who received a wildcard into the WTA title at a 125K Series event, is currently on the comeback trail following an injury-ravaged couple of seasons. Two years ago, she reached a career-high No.71 following victory in Taipei, but since then major operations on her anterior cruciate ligament and Achilles have halted this charge.
Next up will be Miyu Kato, who overcame doubles partner Eri Hozumi, 6-4, 7-6(7). Also advancing were Olga Govortsova, who knocked out No.5 seed Risa Ozaki, 6-1, 6-3, and Dalila Jakupovic, a 7-6(4), 6-1, winner over wildcard Lee Ya-Hsuan.