Sandgren would lose to Marin Cilic at the 2017 US Open after earning his first direct entry. (Getty)
After turning pro in 2011, Sandgren would reach No. 100 in June of 2017, just ahead of his first direct entry into the US Open. That Grand Slam marked the moment he felt he'd "made it".
"I think was when I was like, "OK, I think if I can keep playing well and stay healthy, I can stay here,'" he said. "I think I can get into these majors and some tour events, main draws and qualities of the larger Masters events, and things like that, that's a lot better than where I'd been. So I thought if I can sustain that, that would be great."
The milestone meant a lot after over two decades dedicated to the sport, but also raised bigger questions.
"It was interesting trying to think about what to do after I got inside of [the Top 100]," he said. "That was always my goal was to get inside of 100. It took six years to do that, and it was like, 'What do I do now? What do I do? Do I just moved the marker to 50? Can I do that? Am I good enough?' You just don't know."
He was good enough. In April of 2018, he'd crack the Top 50 just a few months after reaching the quarterfinals of the Australian Open for the first time. Now a little over two years and a few injury setbacks later, he reached the quarterfinals in Melbourne again to put himself back in a similar position at No. 55. Though there was an unexpected hiatus in his progress this season, there's now a stretch of tournaments ahead of him.
At the first one, the Western & Southern Open, Sandgren will next take the court against Felix Auger-Aliassime on Monday.