According to sales data issued on Tuesday by tracking firm Nielsen SoundScan, West's Graduation sold 957,000 copies during the six days ending September 16, while 50 Cent's Curtis trailed with 691,000.
West also bested 50 Cent in the UK.
West's tally is the largest for any album since 50 Cent's previous release The Massacre, which opened to 1.1 million units in March 2005 and spent six weeks at number one.
It surpasses the 860,000-unit bow of West's previous album, Late Registration, which spent two weeks at number one in 2005.
Based on first day sales, pundits had expected West's latest album to sell more than 750,000 copies for the week.
The rivalry between the rappers - which both said was more of a marketing invention than a reality - rekindled faded memories of a time when excited music fans would swamp record stores to snap up new albums.
The music industry has been in a tailspin for the better part of a decade, ravaged by piracy, and it is rare for albums to debut with such hefty numbers.
In fact, for several weeks this year, the top seller sold less than 100,000 copies.
"I am very excited to have participated in one of the biggest album release weeks in the last two years," said 50 Cent, who will forever have to live down a promise that he would retire if West beat him.
"Collectively, we have sold hundreds of thousands of units in our debut week.
"This marks a great moment for hip-hop music, one that will go down in history."
Until last week, the largest sales week of 2007 had belonged to rock band Linkin Park's Minutes to Midnight, which opened to 623,000 units.
The biggest week of 2006 went to country combo Rascal Flatts's Me and My Gang, with 722,000.
Both West and 50 Cent - whose real name is Curtis Jackson - are signed to the world's biggest record company Universal Music Group, which is owned by French media company Vivendi. © 2007 Australian Broadcasting Corporation
