World number one Serena Williams suffered a straight-sets defeat to Eugenie Bouchard at the Hopman Cup in Perth as the United States lost 2-1 against Canada.

The 33-year-old American on Monday recovered from a slow start to see off Flavia Pennetta 0-6 6-3 6-0 and lead her country to a 3-0 win over Italy.

But the following day, Williams - winner of 18 grand slams - registered a costly 23 unforced errors as she suffered a 6-2 6-1 defeat to her 20-year-old opponent in just 50 minutes.

Last year's Wimbledon runner-up Bouchard was delighted to put Canada 1-0 up, and she told hopmancup.com: "It's a good way to start the year. I really want to start the season strong and matches like this help.

"I just want to keep improving as a tennis player. I know how much I still have to improve and that's so motivating to me because I feel like I can achieve my goals and my ultimate dreams.

"I'm just working every single day towards that."