Grigor Dimitrov had struggled through most of the past two seasons and battled with a shoulder injury early this season, but the payoff for his perseverence was sweet indeed.

The 78th-ranked Bulgarian delivered a stunning upset of 20-time Grand Slam champion Roger Federer in the US Open quarter-finals Tuesday, fighting back for a 3-6, 6-4, 3-6, 6-4, 6-2 triumph over the Swiss star who had beaten him in all seven of their prior meetings.

“I wasn't even focusing on Roger. I was focusing on myself,” Dimitrov said.

“I was kind of looking at my dashboard to see where I was at really.” Dimitrov liked the readings, which saw him advance into his first US Open semi-final, matching his career-best Grand Slam run.

He will face Russian fifth seed Daniil Medvedev on Friday for a berth in Sunday's final.

Dimitrov slumped in the rankings due to shoulder pain and a sluggish season, a low so recent and deep the memories are still painful.

“It was not a pretty time. I'm not going to lie,” Dimitrov said.

“It was that low that I don't even want to go there any more. It was just obviously injury, losing points, ranking. That's the lowest point of any player.

“The past six, seven months have been pretty rough for me. But I had somebody to lean on, my friends, my family. I kept on believing again in the work, the rehab I had to put behind my shoulder, the exercise, the practice, fixing up the racquet a little bit.

“There were so many things I had to adjust in such a small but big period of time. Next thing you know, you're almost end of the year, you have a result like that. It's pretty special to me.”

'Nothing to lose'

Dimitrov has had some help from his coaches, retired eight-time Grand Slam champion Andre Agassi and veteran Czech Radek Stepanek, who have both stayed away this week to help Dimitrov focus on his game. “I don't know why, kick my butt a little bit, to wake up or something,” Dimitrov said. “Soon we're going to be reunited but we'll keep things the same for now.” Dimitrov said he has found consistency and worked to control the things he could control, the way he plays.

“Despite the fact that I was losing very tough matches, close matches against players that I shouldn't lose, I kept on believing in the process, kept on working, kept on trying to improve whatever else I had to improve on my end,” he said.

“I really controlled the things that I could. I think that's as simple as that. Sometimes the most simple things are hardest.” Keeping a satisfying victory over a long-time nemesis like Federer in perspective is among those hard things, but Dimitrov is trying to do it.

“I don't want to sound too humble, but it was just another match for me really,” he said. “I don't want to say I had nothing to lose, because I felt I did.

“I just came out prepared the best that I could, especially coming out from the past two weeks of preparation, fitness, good matches. I'm trying to build off that.

“Little by little things are starting to fall into their place. Today was just another step.” His next step could be into his first Grand Slam final.