LONDON—Garbine Muguruza said she lacked energy in her second-round defeat at Wimbledon, and admitted that she has to learn how to balance her training.

The 22-year-old won her first Grand Slam title at the French Open, then fell in the first round of the grass-court event in Mallorca the following week

She was beaten in straight sets by Jana Cepelova at Wimbledon.

"From yesterday I felt already a little bit, you know, tired,” Muguruza said. “…And today during the match, and after the match, I'm like, ‘It's a tough day today.”

She pointed to the effects of her French Open run, saying it was difficult to turn around and play another Grand Slam on another surface in just three weeks.

"It's my first time after doing a great result, coming to another Grand Slam,” she said. “So I'm trying to discover how I'm going to feel. How do I have to go on court? How do I have to rest more? To start after playing [the] French Open, after trying Mallorca—which was too early to start—then practicing hard to come here, I think was a little bit too much maybe. I think at some point my energy was going down.

"So I guess today was the day where I felt it right away."

But she plans to gain from the experience, putting more emphasis on being fully fit for big tournaments.

"I'm going to learn that you really need to concentrate on how to recover,” Muguruza said. “And don't reach a moment where your energy is too low—especially to play a Grand Slam—and to face opponents that, hey, they're good, they're here, they want to beat you so much. You got to be ready. I think I will have to rest more, not keep practicing the same hard [way] to prepare [for] another Grand Slam.

"You don't think, like, practicing 10 hours a day is going to make you play better after you don't have energy."

Muguruza is No. 2 in the rankings.