Serena Williams was happy with her ability to stay focused during a "different and bizarre" US Open first round.

The American world number one lost just five points and was on court for 30 minutes, leading Vitalia Diatchenko 6-0 2-0 when the Russian retired.

Diatchenko appeared to be troubled by a foot injury from the outset and, after Williams won the first eight points of the second set, she retired.

Williams, whose Grand Slam bid started well, said it was one of the stranger matches she had played.

"It was definitely different and bizarre, but at the same time I was still focused," Williams said.

"I kept thinking, you know, just stay focused; don't lose it. You never know what can happen."

Williams will meet Dutchwoman Kiki Bertens in the second round after just a half-hour on court.

Asked if the easy opening match was a worry, Williams said: "No.

"I don't think that's a worry, because my practices are really intense and I really fight really hard in my practices.

"I know that every match is a challenge. I have to be ready for everything."

Williams said she was looking forward to facing Bertens, who beat Mirjana Lucic-Baroni and has never faced the American star.

"Well, I think she's playing well. She does a lot of things well. She has a big serve," she said.

"It's definitely something that I look forward to. See what happens."