The miraculous three-wicket triumph in Mumbai on Tuesday (Wednesday AEDT), which looked impossible when Australia fell to 7-91, confirms Pat Cummins' men will face South Africa in the semi-finals next week.
"After (losing) the first two games, everyone was pretty quick to write us off," said Maxwell, who finished unbeaten on 201.
"To come back and win six straight now is a great effort from this group. The belief is always there and to win a game like tonight, hopefully that belief spreads to the change room."
His side well adrift of the 292 Afghanistan had set for victory, Maxwell partnered with Cummins (12no off 68 balls) to stage a rescue mission on return from a freak golfing accident that left him concussed last week.
Glenn Maxwell needed treatment during his epic match-winning World Cup double hundred.
Maxwell survived a dropped catch and successfully overturned the umpire's call of lbw in the 22nd over and seemed to take the pair of near-misses as a sign to throw caution to the wind.
"I was very lucky and I suppose just made the most of that," he said.
"(The lbw review) was probably the kickstarter I needed to tell myself, 'I need to start playing some shots and be a bit more proactive'."
Shortly after bringing up his second century of the tournament in the 33rd over, Maxwell began battling a back problem that significantly hampered his ability to run.
But the Afghan attack, which had dismissed every other specialist batter for under 25 runs apiece, had no answers as 'The Big Show' lived up to his billing - even on one leg.
At one stage, Maxwell collapsed to the ground, apparently cramping all over, and Adam Zampa lurked at the boundary rope in case the veteran needed to retire hurt.
"I feel shocking," Maxwell admitted.
"I haven't really done a whole lot of high-intensity exercise in the heat and it certainly got a hold of me today."
Glenn Maxwell produced one of the most outrageous knocks in ODI history 💪— ICC Cricket World Cup (@cricketworldcup) #CWC23 | #AUSvAFG pic.twitter.com/rIN8QxDTlmNovember 7, 2023
In the 47th over, Maxwell belted his eighth six to eclipse Shane Watson's unbeaten 184 from 2011 as the best individual ODI innings by any Australian man in history.
By hitting his 10th six over deep mid-wicket, Maxwell, who had hit the fastest-ever World Cup ton off 40 balls against the Netherlands earlier in the tournament, sealed the unlikeliest of wins with 19 balls to spare.
Mitch Marsh (24) was Australia's next-most prolific scorer as Australia pulled off their biggest successful run chase at the ODI World Cup, and pieced together the biggest eighth wicket-partnership in the format's history.
Ibrahim Zadran (129no) recorded the first century by an Afghan player at the World Cup as they posted their highest total (5-291) in any match at the tournament.
In response, Australian opener Travis Head fell for a duck in the second over from Naveen-ul-haq's bowling (2-47).
Azmatullah Omarzai came within an inch of claiming Afghanistan's first-ever ODI hat-trick when he bowled in-form opener David Warner (18) and then had Josh Inglis (0) caught behind.
Maxwell could barely walk, struggling with cramp and a back ailment in his 'unreal' knock.
Panic set in. Marnus Labuschagne (14) was run out with a direct hit after being slow to react to Maxwell's call for a single, before Marcus Stoinis burned a review for lbw and went on six.
But everything changed when Maxwell, Australia's last recognised batter, got his eye in.
Earlier, Australia found wickets hard to come by, with Zampa (1-58) not able to reprise the trickery in the middle overs that had been vital to Australia's resurgence.
Ever-reliable Josh Hazlewood (2-39) had the most luck, while Maxwell (1-55) broke Rahmat Shah's 83-run partnership with Zadran and forced Afghanistan back into their shells.
The Afghan innings was mostly a conservative one until after Zadran brought up his ton. From there, the 21-year-old forged a 58-run partnership with Rashid Khan (35 off 18 balls) across the final four-and-a-half overs.
