Benjamin Becker of Germany serves to Sam Querrey. The American prevailed in straight sets to advance to the quarterfinals. (Matthew Stockman/GETTY IMAGES)

After taking his first ATP Tour title of the year last week at the Farmers Classic in Los Angeles, Sam Querrey came to Washington at the top of his game. But he began the week wondering if the long flight and hot, sticky weather might keep that form from showing up at the Citi Open.

So far, Querrey has been able to keep up the momentum. The 24-year-old American beat Germany’s Benjamin Becker, 6-4, 6-3, on Thursday in a second-round match at the William H.G. FitzGerald Tennis Center in Rock Creek Park. He advanced to a Friday quarterfinal meeting with his doubles partner for the event, Kevin Anderson. The 6-foot-8 South African beat Florent Serra, 6-4, 6-4, earlier Thursday.

“I’m feeling great,” Querrey said after he and Anderson won their doubles match later in the evening. “Every shot feels good and every match I win, I just keep feeling better and better.”

Querrey created buzz in 2010 when he pushed into the fourth round of consecutive majors, including the U.S. Open where he was the last American standing. He was the No. 17 ranked player in the world early last year before a forgettable run capped by an elbow injury kept him out of action most of last summer.

After working hard on his return game and second serve, Querrey’s patience in working his way back is slowly being rewarded. He came into this week ranked No. 38 — his best in more than a year — after jumping 19 spots in the world rankings with his seventh career title.

Querrey, who is seeded eighth at the Citi Open, hasn’t had much luck at this event with just one match win in three previous appearances. He nearly made another early exit this time around, needing a third-set tiebreaker to win Tuesday’s first-round match against Igor Andreev.

But Querrey left little doubt on Thursday, putting Becker on his heels with aggressive play and a first serve that averaged 125 mph. As the match went on, the California native seemed to get stronger and more sure of his game. Querrey broke Becker at love to close the first set and cruised in the second behind an early break. In the final game of the match, he ripped a pair of 126-mph aces.

“Even though I might not be ranked as high as I was at one point, I feel like I’m playing better than I’ve ever played,” Querrey said. “Hopefully, I can just keep winning, keep this going on the right track.”

Later Thursday, top seed Mardy Fish joined fellow Americans Querrey and James Blake in the quarterfinals with a smooth 6-3, 6-1 win over Ricardas Berankis of Lithuania.

Fish, who pulled out of the Atlanta Open last month with an ankle injury and hadn’t played since, dropped a set in his opening match here Tuesday, but he allowed just two break opportunities Thursday and advanced easily.

On Friday, Fish will face Xavier Malisse of Belgium, hoping to advance to the semifinals at this event for the first time in his seventh appearance. The former Olympic silver medalist said he’s excited about playing back-to-back days — and potentially four straight if he reaches the final — as he pushes through an injury he called “manageable.”

“It needs rest, and I’m just not going to give it rest,” Fish said of his ankle. “I can’t give it rest. I don’t want to miss these tournaments” leading up to the U.S. Open.

On the women’s side, fourth-seeded Vania King needed three sets to win a battle of Americans and advance to the semifinals, knocking off seventh-seeded Coco Vandeweghe, 6-1, 3-6, 6-4.

At 5-5, King gave up eight inches to her opponent, but she managed to break Vandeweghe four times, including at love in the final game of the match. King, a 23-year-old who has won 14 WTA Tour doubles titles, will meet top-seeded Anastasia Pavlyuchenkova, who rolled to a 6-4, 6-4 win over Kai-Chen Chang.

“It’s not that complicated,” King said of her plan to combat Vandeweghe’s power. “She’s a great player. She plays fast, but she doesn’t have the wheels that I do.”

The other women’s semifinal will pit third-seeded American Sloane Stephens against unseeded Magdalena Rybarikova of Slovakia.