Andy Roddick has described his loss to South African Kevin Anderson in the first round of the China Open as "unacceptable".

Both players held their serves until the seventh game of the first set, with Anderson breaking his American opponent to record a 6-4 success.

The second set looked to be heading for a tie-break until 25-year-old Anderson produced a decisive late break to win 7-5 and advance through to the second round in Beijing.

"If I break twice and don't win a set that says my serve isn't on," Roddick said. "It's unacceptable."

Roddick, 29, reached the quarter-final of the US Open before being defeated by Rafael Nadal.