Dennis completed a grand slam in the Saturday race in London's east end, leading every lap from pole and securing a victory with a 2.2s margin over title leader Vandoorne - taking a fastest lap in the process.
It was the Warwickshire driver's first win since last year's race in London, but due to COVID last year's races did not have a full crowd in attendance - and Dennis was cheered throughout the race as the fans pulled for a home win.
Reflecting upon his race, Avalanche Andretti's Dennis said that his main task at the beginning was to keep the Mercedes duo of Vandoorne and Nyck de Vries behind him, and manage the gap in the early stages to ensure the two drivers did not work together to get the lead.
Dennis weathered that storm and crucially had more battery life over Vandoorne during the race, meaning he had a buffer in hand to keep the Belgian at bay.
"To replicate what we did last year was absolutely amazing, full house obviously this year with the fans," Dennis said.
"Crossing the line and hearing obviously the British fans was one of the best moments.
"The race itself was pretty challenging at the start; I was just trying to manage Nyck and Stoffel really. Obviously they're team-mates and would work together a little bit, and I feel like we did that quite well.
"Towards end of the race we were pretty in control. We were up on energy and just managing the race, so yeah, really good car.
"Things to work on for sure for tomorrow but nevertheless, we can enjoy this and we've had pretty solid day so very happy for myself and the team."
With the circuit around London's docklands tough to overtake on, Dennis felt that making the most of qualifying left him with most of the job done. Only a late application of fanboost from Vandoorne worried him in the later stages.
He added that the nature of the circuit suited the Andretti package, and that the team had struggled to contend on the faster circuits this season.
"The biggest thing is almost it's quite a technical circuit, so I think we've mechanically got a very good car - it's just when we go to the faster circuits we seem to struggle a little bit more," Dennis explained.
"Generally in the slow speed stuff we've always been good, so this kind of plays into our hands. I'm in a pretty good rhythm around here.
"It's never easy, everyone else behind the top 10 is super fast as well so can you never take anything for granted.
"But just a clean qualifying lap did 80% of the work today, and then just keeping Stoffel at bay and then just managing his fanboost towards the end was really the biggest thing."
