Iowa rallied from a 15-point deficit early in the second half to reach the semifinals of the Battle 4 Atlantis. The Hawkeyes' opponent in the semifinals will be either Tennessee or Texas-El Paso.
Gabriel Olaseni's layup brought Iowa into a tie with 59 seconds to go in the second half and neither side could score the rest of the way.
White tipped in a shot with 1:41 remaining in the extra period to give Iowa a 77-73 lead and Xavier closed within three when James Fair hit 1-of-2 foul shots with 1:15 left.
Xavier then missed two free throws and two 3-point attempts to leave Iowa with the victory.
Roy Devyn Marble led the way for Iowa with 30 points, although he needed 24 shots from the field to do it. Iowa improved to 6-0.
Xavier (5-1) came up with 15 points from Justin Martin.