Serena Williams "disappointed" with winning performance

Serena Williams was left disappointed with her performance against Victoria Azarenka in the US Open third round, despite winning in straight sets.

The number 28 seed demolished the Russian 6-1 in the first, before taking the second 7-5 on a tie-break.

"I think I played really well [in the first set]," said the 29-year-old. "I probably should have kept doing those things. If I was in a zone, it didn't last long.

"I definitely wasn't happy with the way I played today. I was a wee bit disappointed."

The three-time US Open winner takes on Ana Ivanovic or Sloane Stephens in the next round.