The New York Yankees have completed the signing of Alex Rodriguez from the Texas Rangers.
Rodriguez, 28, joins the Yankees in exchange for second baseman Alfonso Soriano and another unnamed player.
Texas will pay $67m (£35.5m) of the $179m (£95m) left on the American League MVP's $252m, 10-year contract.
It is the largest cash sum involved in a major league trade, and baseball commissioner Bud Selig said he did not want it to set a precedent.
"I am very concerned about the large amount of cash consideration involved in the transaction, and the length of time over which the cash is being paid," said Selig.
"I want to make it abundantly clear to all clubs that I will not allow cash transfers of this magnitude to become the norm.
"However, given the unique circumstances, including the size, length and complexity of Mr Rodriguez's contract and the quality of the talent moving in both directions, I have decided to approve the transaction."
The trade comes less than two months after the Yankees' arch-rivals the Boston Red Sox failed to acquire Rodriguez.
The Yankees are the richest team in American sport and the acquisition will push their already astronomical payroll to about $190m.
A New York native, Rodriguez hit .298 with 47 home runs and 118 RBI for the last-place Rangers.
He will move from shortstop, a position at which he has been a seven-time All-Star, to third base, where he will replace the injured Aaron Boone.
The Yankees will keep captain Derek Jeter at shortstop.
Texas will end up paying $140m for three seasons with Rodriguez. The Yankees will owe him $112m for seven years.
Under the deal, the Yankees pay Rodriguez $15m in each of the next three seasons, $16m each in 2007 and 2008, $17m in 2009 and $18m in 2010, according to the AP news agency.
President George W Bush, former owner of the Rangers, told NBC television at the Daytona 500: "I was just as surprised as the Yankee fans and the Boston Red Sox fans when I opened up my paper today.
"It, obviously, is a big deal. A-Rod's a great player and the Yanks are going to be a heck of a team with him in the infield."
The Los Angeles Dodgers have made Paul DePodesta their sixth general manager in less than six years.
DePodesta replaces Dan Evans, who was in the final year of a three-year contract.
The 31-year-old served under Billy Beane as assistant general manager of the Oakland Athletics since November 1998.
His appointment comes three days after the Dodgers' sale from the Fox Entertainment Group to Boston real estate developer Frank McCourt.