Phalula took the lead in the early stages and charged clear with a solo effort to secure victory in 32:57.
Having set the course record of 32:27 last year, she lamented the absence of a timing clock on the lead car, as she had no idea whether she was on record pace while she struggled against the wind.
“I didn’t have any watch to tell me if my splits were good, but I kept on pushing very hard, like last year,” she said.
“It was in my mind that I was under 31-minute pace.”
Had there been an indicator along the route, Phalula felt she could have dipped under her record mark.
“The plan was to run fast from the start, and I thought my pace was better than it was.
“It disturbed me having no electronic clock because I thought I was running harder than last year.”
Her twin sister, Lebogang Phalula, took second place in 33:26 after struggling to keep up with her in-form sibling, with Zimbabwean Rutendo Nyahora ending third, a further 17 seconds off the pace.
Results of the Spar Women’s Grand Prix 10km race in Port Elizabeth:
1 Diana-Lebo Phalula 32:57
2 Lebogang Phalula 33:26
3 Rutendo Nyahora 33:43
4 Nolene Conrad 33:54
5 Rene Kalmer 34:26
6 Cornelia Joubert 34:28
7 Christine Kalmer 36:36
8 Mapaseka Makhanya 34:44
9 Irvette van Zyl 34:49
10 Tebogo Masehla 35:11