The figure was given to the Los Angeles Times by an individual intimately familiar with sales, but unauthorized to speak publicly on the matter. HBO televised the bout.
The network has yet to announce a finalized figure for that novelty non-title boxing match.
On Sept. 16 at T-Mobile Arena in Las Vegas, three-belt middleweight champion Golovkin retained his belts, but saw his perfect record blemished by a draw with Mexico's popular Alvarez, a former two-division champion.
Alvarez, aided by a heavily criticized 118-110 scorecard from judge Adalaide Byrd, wobbled Golovkin with a 10th-round punch and swept the final three rounds, setting the stage for a May 2018 rematch that is already being negotiated.
The sales are the best yet for Golovkin. While Golovkin, 35, didn't exceed 200,000 buys in either of his two prior pay-per-views, Alvarez's loss to Mayweather in 2013 surpassed 2 million buys. Alvarez generated 1 million buys in May while defeating Julio Cesar Chavez Jr. by unanimous decision, and had 900,000 buys in his November 2015 triumph over four-division champion Miguel Cotto.
A Golden Boy Promotions executive declined to comment on the sales figure, and Golovkin promoter Tom Loeffler was not immediately available for comment.