As the U.S. Open turns into the second-week homestretch, former phenom Grigor Dimitrov considered his new-found love of tennis and the idea that simplicity is the key to new possibilities.

“I know how to play tennis,” Dimitrov said after his four-set victory over 36th-ranked Joao Sousa of Portugal. “Just simplicity; that’s the key right now. Just do your stuff, work, go out there and give 100 percent.”

Dimitrov, the 25-year-old Bulgarian who won Wimbledon’s junior title eight years ago and quickly was compared to Roger Federer for his elegant style and potential, has been a regular at Grand Slam events since 2011. But only in 2014 did he have any impact, advancing to the Australian Open quarterfinals and Wimbledon semis.

Since then, he made only one major-tournament fourth round before yesterday, and became known for how often he would switch coaches. Peter Lundgren, Peter McNamara, Patrick Mouratoglou (who now coaches Serena Williams), Roger Rasheed, Franco Davin and now Daniel Vallverdu (who used to coach Andy Murray).

Dimitrov said it’s all about “a change in plan, a change of a bit of mentality. A change of style, that’s too extreme for me.

“You’re always going to hear different voices,” he said. “People that don’t have much of an idea of tennis will say, ‘Hey, man, you should have hit that forehand down the line a bit more.’

“Yeh, man. You want to do it for me. Go ahead.”

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In the last year and a half, Dimitrov said, he “fell in love with tennis again. I started to enjoy the process again, waking up in the morning early to come to practice, doing the ice baths again, pretty much everything.”

He is ready, he said, to face No. 2 seed Andy Murray, who advanced with a four-set victory over Italian Paolo Lorenzi, ranked 40th. Also victorious in a third-round match Saturday was Dominic Thiem, the 22-year-old Austrian seeded 10th. Thiem needed four sets to defeat Pablo Carreno Busta of Spain, ranked 39th.

Also No. 6 seed Kei Nishikori, the Open’s 2014 runner-up, won in four sets against France’s Nicolas Mahut, ranked 42nd.