THE rash of upsets at Wimbledon this week have sharpened the focus of defending champion Serena Williams.

Rafael Nadal was knocked out at the first-round juncture, while Maria Sharapova and reigning men’s champion Roger Federer were dumped out in SW19 on Wednesday.

There were no such shocks on Court One yesterday though, as Williams navigated her way past up-and-coming French teenager Caroline Garcia 6-3 6-2.

The American feels her performance was better than she showed in the first round against Mandy Minella and revealed the shock results elsewhere have acted as a warning shot against complacency.

‘‘The first thing I do is say, ‘Okay, Serena, stay focused’,’’ Williams said.

‘‘This has happened before. I don’t know when. I want to say it was the US Open, though. A lot of players were losing.

‘‘I definitely want to stay focused and stay serious so that’s what I did again yesterday. I was like, ‘Okay, be on your toes and be ready for anything’.’’ Already the overriding title favourite, the exits of second seed Victoria Azarenka and third seed Sharapova have seen one bookmaker price Williams’ nearest rival as far out as 19/1.

The American is not getting ahead of herself though, and in the third round she faces Kimiko Date-Krumm.

The 42-year-old from Japan is the oldest woman to reach the Wimbledon third round in the open era and two years ago faced Serena’s sister, Venus, at the All England Club.

‘‘Kimiko has great handeye co-ordination,’’ Williams said. ‘‘She returns unbelievable shots. It doesn’t matter how hard you hit it, she sees the ball and gets it back.

‘‘She has great hands, has a wonderful great volley, comes to the net a lot, which on grass can be tricky. She plays really flat, so the ball stays really low.’’ It took Venus two hours and 55 minutes to beat Date- Krumm in 2011, edging a deciding set 8-6.

‘‘I did see the match,’’ Williams said. ‘‘I think I lost four years of my life watching that match. So I will definitely be talking to Venus and figuring out what I can do to do the best that I can in my next match.’’ The previous oldest woman to reach round three of the women’s singles in the open era, which began in 1968, was Virginia Wade, who was there to congratulate Date-Krumm as she came off court today.

Date-Krumm says she has been able to maintain her fitness levels by drinking Chinese tea.