Murray, who was playing for the first time in a month, has lost his past seven sets. The slump began with 6-4, 6-2, 6-3 loss to Novak Djokovic in the Australian Open final and continued with a 6-4, 6-1 loss to Marcos Baghdatis in Rotterdam, Holland, in early February.

Against Young, an American qualifier ranked 143rd in the world, Murray wasted early service breaks in both sets and lost his serve four times.

“I started the match well and then when it got close to the end of the first set I just didn't do anything particularly well,” the fifth-ranked Scot said. “I didn't do anything to really lift myself. He started playing better. I didn't find my way back into the match.” Young, a former junior champion who has struggled on the ATP Tour, began the week with a 1-3 match record for the year.

“I thought I played pretty consistent,” Young said. “I got a little nervous. There were some double faults that didn't make it halfway up the net. I've been in this position a couple of times and hadn't won the match. I just told myself this time I was going to see it through and not let the nerves get the best of me.

The tournament's top seeds, Rafael Nadal and Caroline Wozniacki, both won easily. Nadal breezed to a 6-0, 6-2 victory over South African qualifier Rik De Voest and Wozniacki topped American wild card Sloane Stephens, 6-3, 6-2.

Former US Open champion Juan Martin Del Potro of Argentina continued his comeback from a year lost to wrist surgery by ousting defending champion Ivan Ljubicic of Croatia, 5-7, 6-4, 6-2.

Del Potro, No. 4 in the world before his injury, has moved from No. 484 to No. 90 in the past three weeks and is 15-4 on the season.

In other men's upsets, sixth-seeded Spaniard David Ferrer was beaten by Ivo Carlovic of Croatia, 7-6 (3), 6-3, and Marcos Baghdatis, the 19th seed from Cyprus, lost to Somdev Devvarman of India, 7-5, 6-0.

On the women's side, Dinara Safina of Russia beat two-time tournament champion Daniela Hantuchova of Slovakia, 7-6 (2), 6-4. It marked the first time the former world No. 1 has won back-to-back matches since late September.

Safina next plays No. 4 Samantha Stosur of Australia, a 6-2, 6-2 winner over qualifier Laura Pous-Tio of Spain.

In a matchup between two of China's top players, Peng Shuai upset seventh-seeded Li Na, 4-6, 6-3, 6-3.

Also, eighth-seeded Victoria Azarenka of Belarus defeated Ekaterina Makarova of Russia, 6-4, 6-3, and Agnieszka Radwanska, the ninth seed from Poland, beat Iveta Benesova of the Czech Republic, 7-6 (5), 6-4.