Rune upset by Marozsan in Miami, Shelton advances
The convincing victory, in just 59 minutes, was a third win against a top-10 opponent in a Masters event for the 57th ranked 24-year-old.
Marozsan dominated his Danish opponent from the outset, striking 23 winners and saving all three break points that he faced.
The Hungarian's two previous wins against top 10 opponents in this level came when he beat Carlos Alcaraz in Rome and Casper Ruud in Shanghai last year.
"I enjoy playing at the highest level, I had a great day and enjoyed every moment on the center court against a very talented player," said Marozsan.
"I tried to put more pressure on him and I played very high intensity tennis and maybe he didn't find the way to come back or do something different," he said.
Marozsan will face Alexei Popyrin in the third round after the Australian beat Czech Jiri Lehecka 6-4, 6-4.
After three of the top four ranked Americans were exited the tournament on Saturday, Ben Shelton kept the Star Spangled flag flying in Florida with a 6-3, 6-4 win over Spanish teenager Martin Landaluce.
Shelton did not face a break point in the contest and won both sets with unstoppable aces down the middle.
"I thought I was pretty complete today,” said Shelton. "I thought I did a great job backing up my serve and usually when I have a lot of confidence and holding easily, the rest of my game continues to flow, and my confidence just grows. I think that helps me a lot and puts a lot of pressure on the other guy," he added.
In the third round, Shelton will be up against 23rd seed Italian Lorenzo Musetti, who defeated Russian Roman Safiullin 7-5 6-1.