Envision driver Frijns finished just over one second behind Cassidy at the chequered flag, having shadowed the new championship leader for the majority of the 36-lap contest.
Frijns had initially taken the lead from polesitter Oliver Rowland at the start and led the opening four laps before taking his first Attack Mode activation.
Unable to regain the lead after Cassidy had used both his activations, the leading pair were more than six seconds clear of Rowland at one stage, such was their pace and use of energy.
“The start was pretty good, took the lead and then I was fighting Nick,” said Frijns, who took his first Formula E podium since New York in 2022.
“On pure pace we were almost killing each other halfway, which was quite nice, it was really a challenge.
“I think Nick was just a bit too strong for me today, he just had that little edge on me.
“But as he said as well, everybody has their day, I just didn’t have mine yet but hopefully it’s coming quite soon.”
By the mid-point of the race, Cassidy dropped his pace considerably to conserve energy, backing Frijns into Rowland and the chasing pack as he managed a lead of no more than a few car lengths for the remainder of the race.
“I didn’t always feel that,” Cassidy told Autosport when asked if he had the lead in control in the latter stages.
“My energy target was super low; him [Frijns] and I were going at it at the start but it was nice to be able to drive like that at the start of the race and try and make a difference and I think we did.”
Cassidy leads the championship standings by 19 points, having stood on the podium in all three races of the Formula E season so far. He finished third in the Mexico City E-Prix and in the first race in Diriyah.
The Kiwi believes the start to his first season with Jaguar has exceeded expectations so far, having never previously performed that well in Mexico and Saudi Arabia previously.
“It is the dream start, I hadn’t had a podium here or Mexico before,” he said.
“I think my best result at this track was sixth across the last six races. It’s definitely above expectations.
“It’s not really been a track for me for whatever reason so I genuinely thought I would struggle. Like every race, though, I work as hard as I can and try to be better.
“I wasn’t the ultimate quickest in qualifying today, but I think honestly in the race I probably was.
“I felt really good in the race and it was really nice to be able to lead for that long.”
