A pre-election poll suggested she could wind up with nearly two-thirds support.
But even in defeat, Obama was on track to gain at least 14 delegates, bringing him within 50 of the 2,118 needed for the nomination.
Aides to the 46-year-old Illinois senator are predicting he will clinch the long-sought prize within days.
Montana and South Dakota hold primaries on Tuesday, the last of the primary campaign season.
