Sam Querrey never hit rock bottom, but his frustration level nearly reached its tipping point.

Five straight first-round losses and more than two months without a victory prompted a period of introspection from the 19-year-old Thousand Oaks resident.

After returning from Wimbledon in June, Querrey sat down with his parents and his coach and took stock of his status.

"I might have gotten a little content at where I was and became lackadaisical," Querrey said. "I kind of kicked myself in the butt at that point and started working harder and acting more professionally."

The pep talk, along with a change of surface to his favored hard courts, reinvigorated Querrey's spirit. The 6-foot-6 right-hander has gone 10-4 since leaving London, and enters the U.S. Open this week at an all-time high.

Only 14 months into his professional career, Querrey broke through into the top 50 of the rankings last week at No. 47.

"I would have never thought I would be that high a year ago," said Querrey, who plays Austria's Stefan Koubek in the first round in New York. "Eventually I thought I would get there, but not at this point in my career. It's really cool."

But reaching the career high required Querrey to endure a few lows during his first professional foray on clay and grass.

Of his nine losses on the surfaces, five were three-setters and one was a five-setter.

"I had done so well at the beginning of the year, and I expected myself to just keep rolling and go far in tournaments," Querrey said.

"All of a sudden it just wasn't happening, and I was losing some tough matches."

Although he expected Querrey's performance on grass to be better, Grant Doyle wasn't surprised his star pupil hit a lull.

"Things happened so quickly for him at the start, that once he got a couple of losses he got a little frustrated," said Doyle, who has been coaching Querrey for nearly four years. "But everyone out here goes through stages, and you are going to lose to tour-level players."

Once Doyle and Querrey's parents emphasized the commitment necessary to be a professional athlete, Doyle noticed an immediate change in Querrey.

"He is emotionally invested in this game now," Doyle said. "He is working harder in the gym and his practices are a lot more focused.

"He is more focused during matches and playing less games that are loose. He doesn't give away games like he used to, and it makes him that much tougher."

The results on the court finally started turning Querrey's way again in late July, when he reached the semifinals in Indianapolis with victories over Julien Benneteau, Ivo Karlovic and James Blake.

Instead of participating in the Legg Mason Tennis Classic in Washington D.C., Querrey chose to play a Challenger event in Vancouver, British Columbia, and reached the final. His momentum continued with a quarterfinal appearance in Cincinnati three weeks ago.

"I hit my comfort zone, and I have been rolling ever since," Querrey said. "It feels good to be winning some matches again."

After spending a few days at home in Thousand Oaks, Querrey flew to New York last Thursday to prepare for his first meeting with Koubek.

"I am looking forward to it," Querrey said. "Obviously he is a great player and has been around for a while so he knows how to win. I just have to stay levelheaded the whole time and serve well and keep the ball to his backhand."

Querrey won't make any bold proclamations about his Open expectations. But after emerging from his recent professional rite of passage, he believes he's mentally stronger to handle whatever comes his way.

"I learned a lot from it," Querrey said. "I think in the long run it might have been a good thing."