That is the prediction of Paul Kane of the Washington Post - though it is easier to find where his point is picked up on political wire - because of how even the race is, and because Dem primaries are not 'winner-take-all'. Unless a neck-and-neck race turns overnight into a landslide, the super-delegates will come into play.
Do the math. If they both have about 900 pledged delegates so far, they need to win more than 1,100 of the remaining 1,400 delegates to win the nomination through actual voting.
Of course, there are lots of versions of that scenario. The elections will have an impact on the super-delegates' choices, especially if either candidate can open up a lead. But both campaigns may shift up a further gear on the micro-targetting and arm-twisting as much as the public campaign.