But if he had won the votes of a majority of the far-right leaning party delegates at the state GOP convention Saturday, he would have bypassed a primary altogether.
Romney sought to put a positive spin on the convention vote and the need for a primary.
GOP voters will decide between the two in a June 26 primary.
The 2012 Republican presidential nominee and former MA governor is considered the favorite to succeed retiring Sen.
The Tribune reported that Romney blamed the results on discontent with his decision to also gather signatures to secure a spot on the primary ballot.
Mr. Kennedy, a doctor and lawyer who has been a state lawmaker since 2013, received applause from the crowd as he criticized the national debt, Common Core education standards and President Barack Obama's health care law.
The delegates in the convention tend to become more conservative than Utah'therefore electorate, " the newspaper noted.
The issue prompted hours of debate, shouting and booing at the convention. Majority have been political newcomers who questioned Romney's criticism of President Donald Trump and the depth of his ties to Utah.
On Saturday, Romney told CNN he didn't know yet whether he would support Trump's 2020 re-election campaign, leaving him room to promote himself as an independent voice for Utah.
"I'm with the president's domestic policy agenda of low taxes, low regulation, smaller government, pushing back against the bureaucrats", Romney said.
Stay-at-home mother Michelle Cluff said she liked Romney's experience and believes he is ready to get to work as a senator. "You don't have to be high-powered and connected to Washington, D.C., to actually offer your services to the people", Kennedy added.
A former MA governor, he ran for president in both 2008 and 2012.
"I have chose to run for United States Senate because I believe I can help bring Utah's values and Utah's lessons to Washington".
During the 2016 presidential race, Romney called Trump a "con-man" and a phony.
After previously saying he wouldn't accept an endorsement from the president, in February Romney happily accepted Trump's support for his Senate bid.