Serena Williams returns to tennis court

Serena Williams grabbed her racket and got out on a tennis court Tuesday, which she said was her "first day back" after a series of health problems, including blood clots in her lung.

The 13-time Grand Slam singles champion and former No. 1-ranked player has not played an official match since she won the title at Wimbledon in July.

Shortly after claiming her fourth singles championship at the All England Club last year, Williams cut her foot on glass at a restaurant, an injury that led to two operations. The second surgery was in October, and she said she spent 10 weeks in a cast and 10 weeks in a walking boot.

The 29-year-old American was diagnosed in February with blood clots in her lung. After that, she said she needed treatment for a hematoma — a gathering of blood under the skin — on her stomach.

Williams has not said when she might return to competition.

Roger Federer started his clay-court season Tuesday by dispatching Philipp Kohlschreiber of Germany, 6-2, 6-1, with precise shot-making at the Monte Carlo Masters.

In other matches, Ivan Ljubicic defeated Jo-Wilfried Tsonga of France, 7-6 (2), 6-4, and Milos Raonic downed Ernests Gulbis, 6-4, 7-5. Tomas Berdych defeated Olivier Rochus, 6-2, 6-3, to set up a match against Ljubicic.

Barcelona, Manchester United advance to Champions League semifinals

Lionel Messi scored his record 48th goal of the season Tuesday to give Barcelona a 1-0 victory over Shakhtar Donetsk of Ukraine as the Spanish club advanced to the semifinals of soccer's European Champions League for the fourth successive season.

Barcelona, a three-time European champion, had won the first leg of the quarterfinal series, 5-1, at home and took the series, 6-1 on aggregate, after the win in Donetsk.

Manchester United, another three-time champion, also reached the semifinals by completing a 3-1 aggregate win over Chelsea. Goals by Mexico's Javier Hernandez and South Korea's Park Ji-Sung gave Manchester a 2-1 win in Manchester, where Didier Drogba scored Chelsea's lone goal. Manchester had won the first game, 1-0, in London on a Wayne Rooney goal.

The quarterfinals conclude Wednesday with home games for Tottenham Hotspur, which trails nine-time champion Real Madrid, 4-0, and Schalke '04 of Germany, which leads defending European champion Inter Milan, 5-2.