Defending Wimbledon champion Serena Williams has insisted she is not burdened by the pressure of chasing a 22nd grand slam title to emulate Steffi Graf.

Williams swept past Amra Sadikovic 6-2 6-4 at Wimbledon on Tuesday, to book a second-round clash with fellow American Christina McHale.

The 34-year-old has stalled on 21 major titles since claiming her sixth crown at SW19 last year, but remains bullish about her chances of drawing level with Graf's open-era record.

"I think more or less about winning Australia, I think about winning the French Open; didn't happen," said Williams.

"I think about winning Wimbledon. I don't necessarily think about winning 22.

"Mentally I've been further down than anyone can be. Well, maybe not anyone, but I've been pretty low.

"There's nothing that's mentally too hard for me."

Williams eased to her 80th career victory at Wimbledon to open Tuesday's Centre Court programme, in a straight-sets win where she was rarely troubled by the world number 148.

The top seed then rejected any notion of struggling under the weight of expectation or grand slam pressure in that continued bid to catch Graf.

"Obviously it means a lot to me, probably means more to me than to anyone, anyone," said Williams, talking about her determination to continue winning major titles.

"It's definitely something you just have to deal with.

"It's coming to a way that you deal with it. It's 'how are you going to deal with it'?

"For me it's dealing with it the best that I can."

Former world number one Caroline Wozniacki will drop out of the top 50 after her straight-sets, first-round defeat to Svetlana Kuznetsova at Wimbledon.

World number 14 Kuznetsova dispatched Denmark's Wozniacki 7-5 6-4 on Centre Court on Tuesday, to book a second-round clash with British wild-card entry Tara Moore.

Wozniacki rose to number one in the world in 2010, managing to hold the top spot for 67 weeks.

But the 25-year-old has been unable to maintain that stellar form, and will doubtless view this latest setback as a big frustration.