The Norway forward is the quickest player ever to score 40 goals in the competition – reaching the milestone in just 35 matches, 10 fewer than Ruud van Nistelrooy, the previous record holder.
His goal also sparked a comeback win that ensured City, already through to the last 16, secured top spot in Group G with a game to spare.
For an uncomfortable 40 minutes, it looked as though their proud 28-match unbeaten home European record was about to come to an end.
But the second-half introductions of Julian Alvarez and Jeremy Doku transformed City.
Within seconds, Alvarez had sent Haaland through to half the deficit – and with Doku’s running unbalancing the Leipzig defence, Phil Foden took advantage of the space he found after collecting Josko Gvardiol’s inside pass to level.
Three minutes from time, Alvarez completed the fightback, steadying himself eight yards out before delivering a precise finish to the corner after Foden had provided the cross.
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The defeat was tough on Belgian forward Lois Openda, who cost Leipzig a club record fee when he signed from Lens in July – one that could reach 45m euros (£38.95m).
And he showed his quality with an excellent first-half double that had raised hopes of a shock win for the visitors on the ground where they lost 7-0 in last season’s knockout phase.
Haaland’s great goalscoring feats continue
The first half must have brought back uncomfortable memories for Gvardiol. As the Croat recounted in the build-up to the game, he was part of the Leipzig squad beaten by seven goals in this stadium earlier this year in a one-sided last-16 game.
Having switched between the clubs for £77m in August, Gvardiol might have hoped for a happier experience this time.
And it was in the end – but only after a tough opening half. He was the man Openda stepped inside to drive his low shot past Stefan Ortega for Leipzig’s second, even if the blame belonged to Ruben Dias, who lunged into a tackle by the touchline on the halfway line to allow a clear run for the forward.
Close by, City manager Pep Guardiola waved his arms in that familiar dismissive fashion, which suggested he was not happy.
That reaction was similar to the one that had followed Openda’s opener. On that occasion, Manuel Akanji had tried to block the striker from reaching a bouncing ball on the halfway line. Although he succeeded in that mission, the Swiss defender did not think his opponent would simply spin away from him and on to the loose ball, which he tucked neatly into the corner.
Rico Lewis and Haaland both drove over from central positions before the break. Haaland’s thunderous effort in particular suggested he was not happy at the state of affairs.
It was not to last.
Instead, Haaland took his tally for the campaign in all competitions to 19. That means he now has 71 in less than a season and a half.
Once the Norwegian had scored, there was an inevitability about what was to come.
City will be sure of playing their second leg at home when the draw for the last 16 is made next month and few will argue against their chances of becoming the first English side since Nottingham Forest in 1980 to successfully defend what used to be known as the European Cup.