WASHINGTON (AP)—Sam Querrey made two double faults at crucial times and Janko Tipsarevic took advantage to upset the sixth-seeded American 7-6 (3), 6-3 on Wednesday in the second round of the Legg Mason Tennis Classic.

After a fault to open the first-set tiebreaker, Querrey tried for a second-serve ace with a booming serve that missed, and he never recovered. He double-faulted again on break point to give Tipsarevic a 5-3 lead in the second set. Tipsarevic didn’t give Querrey any chance to recover, serving three straight aces in the next game to seal the match.

“I was making a lot of errors all match,” Querrey said. “He was forcing me to go for a lot of shots. I was tired, so I was trying to end points a little sooner by going for some bigger shots.”

Querrey was one of four seeded players to lose in Wednesday’s first four matches. No. 9 seed Ernests Gulbis retired after falling behind Illya Marchenko 6-1, 1-0 due to heat—the temperature was above 90 degrees when play started—and Marco Chiudinelli beat No. 10 seed Radek Stepanek 6-1, 6-3.

Alejandro Falla advanced to the third round when Lleyton Hewitt, seeded 11th, also retired due to a right calf injury. Falla was leading 7-5, 3-2 when Hewitt pulled out.

No. 8 seed Marcos Baghdatis broke the pattern, advancing with a 7-6 (3), 7-6 (5) victory against Horacio Zeballos.

Querrey battled fatigue in the hot and humid afternoon weather. It was his first match of the tournament after a first-round bye, and he was coming off a string of tough matches that culminated with a tournament win at Los Angeles on Sunday.

It was the second time the two had met in less than a week. Querrey beat Tipsarevic in a tight three-set match featuring two tiebreakers in the semifinals at Los Angeles. Tipsarevic knew Querrey was struggling in the rematch when the American struck some of his second serves with his full first-serve power even before the tiebreaker.

“I said, he’s getting tired, just hang in there and it’ll come,” Tipsarevic said. “And it did come. Winning a first point in a tiebreak on a guy’s double-fault when he’s trying to make an ace on the second serve shows you he’s getting tired, and if you stay disciplined you have a bigger chance to win.”

Tipsarevic had no problems with his service game. The Serb finished with 16 aces, and only lost six points all match when serving.

“I like to think of myself as one of the better servers out there for my height,” the 5-foot-11 Tipsarevic said. “But today was a little bit more than expected.”

Querrey’s big week also included a Tuesday morning tennis clinic on the White House lawn—and a surprise appearance by President Barack Obama.

“No one saw him coming, he kind of snuck around,” Querrey said. “It was pretty cool.”

The sixth-seeded Querrey is the highest seed not to make it past the second round so far. Top-seeded Tomas Berdych of the Czech Republic is scheduled to face Dmitry Tursunov in Wednesday’s last match.