The Andretti Autosport driver had built up a margin of three-tenths over the opening two sectors in the final duel and posted a 1m37.986s.
Cassidy, who finished second in Saturday’s opening Rome E-Prix but took the championship lead from Dennis as a result, put in an impressive final sector to slash the margin but fell 0.071s short at the line.
Dennis also receives three points for his pole position, which moves him to within two points of Envision Racing's Cassidy in the standings, but the result remains provisional as the Briton is under investigation for an impeding incident in his qualifying group.
Mitch Evans, the victor in Saturday’s Rome E-Prix which propelled him into title contention, was finally beaten this weekend as championship rival Cassidy got the better of his fellow Kiwi despite a sketchy moment through Turn 7 as both set scrappy semi-final laps.
Just over a tenth separated Dennis and Nissan’s Norman Nato in the second semi-final duel as the Briton’s lap, a 1m38.087s, was just 0.031s slower than Cassidy’s time in the same element of qualifying.
Two strong final sectors ensured Dennis of a semi-final spot after finishing nearly half a second ahead of Maximilian Gunther, the Maserati driver also under investigation after the session for not slowing down through a yellow flag zone in his qualifying group.
The fastest time through all three sectors meant Cassidy comfortably beat NIO 333’s Dan Ticktum in the opening quarter-final duel by more than a second with a 1m37.536s.
Source: Autosport