Some good news for Hatch: In the primary subset who identify themselves as Republicans, he is ahead by a slightly better 51%-35%. However, Chaffetz has an identical lead of 51%-35% among those who identify as "very conservative" -- a demographic likely to participate in the caucuses for the crucial state GOP convention.
In 2010, Hatch's fellow Senator Bob Bennett was defeated for renomination at the convention, unable to even advance to the primary between eventual winner Mike Lee and his opponent Tim Bridgewater.
In order to win a party nomination in Utah, candidates must compete at the state party convention, in which it is possible to win the nomination outright with a 60% vote of delegates. Otherwise, the top-two finishers head to a runoff. See here for more on the rules, and for the moment when Bennett was eliminated in 2010.