Saint Joseph's first game as the nation's No. 1 team was also its first loss of the season, a shocking 87-67 collapse against unranked Xavier in the Atlantic-10 quarterfinals Thursday.

The Hawks came in with a 27-0 record, three victories from becoming the first team since 1991 to enter the NCAA Tournament undefeated. But they trailed Xavier by as many as 34 points, and the upset raises questions about how serious a contender the tiny Philadelphia school will be for the national championship.

In addition to possibly costing Saint Joseph's a top seeding at the NCAAs, the rout tarnishes a magical run by a team that was one of the biggest surprises in sports this year.

Romain Sato led Xavier with 24 points and 11 rebounds, while Lionel Chalmers scored 23, and Anthony Myles 19.

Saint Joseph's star backcourt of Jameer Nelson and Delonte West were held to a combined 11-for-35 shooting, and they scored 16 points each. Xavier made 71.1 percent of its shots, while holding Saint Joseph's to 35.4 percent -- its worst showing all season.

At one point, Saint Joseph's was limited to one field goal over more than 10 minutes. And the Hawks' biggest weakness was exposed by the Muskateers (21-10), who built a 43-18 rebounding edge.

Xavier will play Rhode Island or George Washington in the semifinals Friday night.