Shohei Ohtani's 50th home-run ball has sold at auction for nearly $A6.6 million, a record price not just for a baseball, but for any ball in any sport.

Ohtani became the first player in baseball history to hit 50 homers and steal 50 bases in a season, reaching the milestone on September 19 when the Los Angeles Dodgers star hit his second of three homers against the Marlins.

"We received bids from around the world, a testament to the significance of this iconic collectible and Ohtani's impact on sports, and I'm thrilled for the winning bidder," Ken Goldin, the founder and CEO of auctioneer Goldin Auctions, said in a statement.

The auction opened on September 27 with a starting bid of $US500,000 ($A750,000). The auctioneer said it could not disclose any information about the winning bidder.

The auction has been overshadowed by litigation over ownership of the ball. Christian Zacek walked out of Miami's LoanDepot Park with the ball after gaining possession in the left-field stands. Max Matus and Joseph Davidov each claim in separate lawsuits that they grabbed the ball first.

All the parties involved in the litigation agreed that the auction should continue.

Matus's lawsuit claims that the Florida resident - who was celebrating his 18th birthday - gained possession of the Ohtani ball before Zacek took it away.

Davidov claims in his suit that he was able to "firmly and completely grab the ball in his left hand while it was on the ground, successfully obtaining possession of the 50/50 ball".

Ohtani and the Dodgers are preparing for Game 1 of the World Series against the New York Yankees, scheduled for Friday night (Saturday AEDT).