Serena Williams has admitted that she 'got a little tight' during her US Open match with Kiki Bertens.
The world number one, who is searching for the calendar Grand Slam, almost dropped the opening set against the Netherlands hitter before eventually winning 7-6(5) 6-3, but the 21-time major champion has insisted that she is not worried about her slow start.
The 33-year-old is quoted by BBC Sport as saying: "It definitely doesn't worry me. I think being down a lot, I know I can try to make a comeback.
"I've been really relaxed, but today I was a little tight and and I think it showed."
Williams will play compatriot Bethanie Mattek-Sands in the last 32.