Updated

The fairy tale run for Monica Puig that included a gold medal at the Summer Olympics in Rio and even greater expectations at the final Grand Slam tournament of the year came to a crashing halt in a first-round upset on Monday night.

The 22-year-old Puerto Rican, who was seeded 32nd at the U.S. Open, lost in straight sets to Zheng Saisai of China.

While visibly upset while talking to reporters after the match, Puig emphasized that the loss does not take away the amazing year she has had thus far and it will only push her even more to learn from the mistakes for future tournaments.

“These are new waters for me, new territory,” she said. “I’m going to have to start getting used to it.”

When Puig took to the court on Monday, with plenty of boricuas cheering her on from the stands, she knew that expectations were great.

However, she failed to replicate the magic that ignited in Rio de Janeiro just two weeks ago, falling 4-6,3-6 to Saisai. She struggled to maintain her service game, winning just 45 percent of points on first serve. She also had 28 unforced errors.

“She played well. She complicated me,” Puig said, adding, “I’m playing well. I feel good about my game.”

She added: “I know what type of game I want to play. I want to finish the year off with a high. I’ve had a great year before that.”

Puig noted that she is not the only player in the sport to follow a successful tournament run with a less-than-stellar performance. She even mentioned Angelique Kerber, the German player she beat in the gold-medal match, who was able to come back from a draining Olympics to make it into the final at Cincinnati just last week.

"She's been there," Puig said. "She knows what it's like. She knows she's No. 2 in the world. She's tested the waters out a little bit.”

"I'm brand new to this,” she added.

For Puig, Monday’s night loss is a learning experience: about getting up, brushing yourself off and getting back to work.

"I need to keep racking up as much experience as I can," Puig said. "You know what? This isn't going to be the last of me. I know I'm going to keep working hard. The Olympics was something that happened because of all my hard work.”

Elsewhere at the Open, Spaniards Rafael Nadal and Garbine Muguruza earned their tickets into the second round.

Nadal, 30, who is recovering from a wrist injury, acknowledged after the game that he could use some more time rest, but that he played well against Denis Istomin.

"Not easy to go 2½ months out of competition, in the middle of the season, without hitting a forehand," Nadal said. "I need to have the confidence again with my wrist.”

As for French Open champion Muguruza, she complained about having trouble breathing after dropping the first set of the match she would go on to win in three.