The Andretti driver had climbed from 10th on the grid to challenge for victory and led at several points during the 34-lap contest in Brazil on Saturday.
The Briton found himself back in third after taking both Attack Mode activations, admitting that “communication wasn’t great” between himself and the team to capitalise on the strategic element.
“I think the win was there,” Dennis told Autosport. “That second Attack Mode was quite unclear from my side.
“I got told to take it when we still had attack, [mode] so it would have been a failure of Attack Mode, then I got a late call to cancel it and then I took it again. It was all a bit of a mess.
“It just wasn’t very clinical between me and the team, the communication wasn’t great.
“We move on and we learn from it and I think we’ll be better prepared if we’re in that situation again.”
Despite having more energy than both eventual winner Sam Bird and runner-up Mitch Evans ahead over the final laps, soaring internal car temperatures meant Dennis began to lose power and drop back.
It put him into the clutches of polesitter Pascal Wehrlein, with the Porsche driver lunging up the inside of Dennis into the final corner on the last lap.
The tight line meant both lost momentum on the exit, allowing Nissan’s Oliver Rowland directly behind to sneak ahead on the run to the chequered flag as Dennis slipped to fifth.
“He [Wehrlein] went for a gap and I was probably about 100bhp down at the end to the other guys, I was so slow down the straights,” added Dennis.
“There’s obviously only so much you can do and they had such a speed advantage over you and they punished us and obviously Oliver got the best out of it.”
Rowland had started one spot behind Dennis in 11th but made steady progress through the field, passing Jean-Eric Vergne into Turn 1 on lap 30 for sixth, and moved up another spot at the expense of Antonio Felix da Costa two laps later.
He then closed on both Dennis and Wehrlein quickly with his last-lap, final corner overtake making it back-to-back podiums for the Briton.
“To be honest, when I was in fifth it already felt like Christmas,” said Rowland.
“I could see the other two were struggling more than I was [with battery temperatures] but I was quite concerned to just finish the race myself.
“I saw them fighting into Turn 7 and I thought I’d just get close and if anything happens, I can pick up the pieces.
“They were pretty aggressive on each other and put each other right on the inside for Turn 11 [the final corner] and I managed to get up underneath them and beat them to the line which was pretty cool.”
