Guenther timed things just right, happy to hold fire behind Jake Dennis (Avalanche Andretti) once the Brit had taken the lead through the first round of ATTACK MODE activations.
The telling switch came as Guenther held off on his second jolt of ATTACK MODE when Dennis blinked first. The German was able to generate a gap enough to leapfrog the Avalanche Andretti driver by the time he made the dive for his final 50kW boost on Lap 18.
From there, the Maserati MSG Racing driver didn't look back and, in fact, was able to stretch his legs - pulling out 2.822 seconds on Dennis come the flag and more than 18 seconds on third-placed man Mitch Evans in the Jaguar TCS Racing I-TYPE 6.
Nobody had won by more than two seconds in the GEN3 era since Dennis' season-opening victory in Mexico City and that margin was the largest we'd seen in the last 10 rounds. That marked Maserati's first world championship single-seater win since Juan-Manuel Fangio's legendary victory at the Nurburgring all the way back in 1957 - history made.
Drama struck the standings leader heading into Round 11, Nick Cassidy. The Envision Racing driver had only failed to score once this season, with 13th in Diriyah, but he made a costly slip in trying to pass his then-nearest title rival Pascal Wehrlein (TAG Heuer Porsche) on Lap 20 - coming off worse for wear, shuffled to the back of the pack and 19th position with damage.
That would prove doubly costly given Dennis' second-placed finish and Wehrlein's drive to sixth - the German backing up his win on Saturday with another strong haul of points after a measured drive.
The Nissan pair of Sacha Fenestraz and Norman Nato made late-race strides to seal fourth and fifth from seventh and 12th on the grid, respectively. The French-Argentine's move on reigning champion Stoffel Vandoorne (DS PENSKE) was particularly eye-catching - catching the Belgian unawares into the hairpin, with his teammate Nato able to follow.
That pass saw Vandoorne shuffled back to an eventual ninth as Wehrlein, Antonio Felix da Costa (TAG Heuer Porsche) and Edoardo Mortara (Maserati MSG Racing) able to waltz by for sixth, seventh and eighth. Envision Racing's disappointing afternoon saw only a point head their way, with Sebastien Buemi rounding out the top 10.
All that left the standings top three split by just six points with Wehrlein on 134, Dennis 133 after that fourth consecutive podium and Cassidy on 128 after a disastrous afternoon for the Kiwi. TAG Heuer Porsche head the way in the Teams' running with 212 points - pulling further clear of Envision Racing who sit on 190 points with Jaguar TCS Racing third on 171.
Season 9 has five races to run, with a first trip to Portland, Oregon in the United States next up in three weeks' time on 24 June.
As it happened...
Guenther led into Turn 1 from pole while Dennis fended off Evans, despite the Kiwi briefly getting ahead, and Fenestraz - the French-Argentine leaping from seventh to fourth off the line.
Lap 4 saw leader Guenther jump through the loop for two minutes and the first of his two eight-minute total ATTACK MODE boosts - the first of the lead group to do so, with Dennis going a lap later and leapfrogging the German in the process. Evans took his first 50kW boost another lap later - leaving Dennis in the race lead once it all shook out.
Lap 9 and Evans pulled a blinding dummy on Guenther into Turn 1, sending the Maserati one way while diving up the inside of Turn 1 for second spot. Mortara did likewise to make it beyond reigning champion Vandoorne for fourth, in quick succession. Guenther didn't let it lie there, though. A lap later, he squeezed back by the Jaguar through the tight, twisty middle sector of the lap at Turns 9 and 10, then set about leader Dennis.
Once again, the fast, flowing Ancol Beach Circuit produced a cagey middle portion of the race as leader Dennis looked to bank as much energy as possible without giving up P1 and track position. The Brit positioned the car expertly to keep Guenther and Evans back while expending as little effort as possible. Dennis led Guenther, Evans, Mortara, Vandoorne, Fenestraz, da Costa, Wehrlein, Cassidy and Nato the top 10 on Lap 14.
The second round of ATTACK MODE activations began with Vandoorne, Fenestraz and Wehrlein heading through the loop for six, two and two minute 50kW boosts, respectively. The leaders hung on for another lap with Dennis blinking first and battling hard to scythe straight back by Evans while Guenther scrambled clear in the lead - the German getting the hammer down to make a gap and leapfrog Dennis for what would be a net lead when Evans' would head for his second ATTACK MODE boost.
Dennis knew he had to make amends and on Lap 19, he tried to go all the way around the outside of Guenther - looking to catch the Maserati driver unawares late on the brakes into Turn 1. Guenther was boxed in by leader Evans on the inside and the dirty part of the track but he was able to squeeze Dennis wide and hold fast.
On Lap 19, drama struck for standings leader Nick Cassidy. The Envision Racing driver made a rash attempt at a move up the inside of Porsche's Wehrlein when it didn't look on. He clipped his front wing and could recover only to 19th and last position. Could that attempt prove costly in the title race and be a move the Kiwi regrets come the final chequered flag of the season?
On the next tour, leader Evans had to jump for his final ATTACK MODE activation, leaving it a straight fight between Guenther, Dennis and himself the top three all on equal energy, with Wehrlein likely content to pick up any pieces from a net fifth, with his closest title rival out of the running.
On Lap 23 it looked as if the lead pair of Guenther and Dennis had checked out with Evans unable to live with their pace. They broke three seconds clear to set up a one on one fight to the flag for the win. From there, though, Guenther was able to draw out two seconds on even Dennis - surprising given the race pace we've seen from the Porsche 99X Electric's so far this season.
Into the final stages of the race and Lap 30, Guenther was able to hold Dennis at arms length some three seconds behind, while the Maserati racer had pulled 10 seconds out on the factory Jaguar of Evans - no mean feat.
The fight heated up further back, with Fenestraz lunging up the inside of Vandoorne, surprising the Belgian into the Turn 13 hairpin, with his Nissan teammate Nato following suit with Wehrlein profiting just a few turns later. Fourth to seventh in just a sector for the reigning champion who was caught unawares. A lap later and the Season 8 champion was 10th and on the brink of falling out of the points entirely, with da Costa, Mortara and Ticktum all making it by the DS PENSKE driver.