And two apologies. And counting.

Serena Williams and her sister, Venus, last night claimed their 10th grand slam doubles championship by brushing off the challenge of Cara Black and Liezel Huber 6-2, 6-2.

The more difficult situation for Serena lies, of course, off court after her rant at a lineswoman in her semi-final defeat by Kim Clijsters on Saturday night. Serena was fined $10,000 for the verbal abuse and a further $500 for racket abuse by the USTA but the matter is not yet resolved.

Bili Babcock, executive director of professional tournaments for the ITF, confirmed yesterday that he had started an investigation into the incident when the world No.2 pointed her racket and swore at a lineswoman after she was called for a foot fault. The immediate penalty of a dropped point sent Clijsters through to the final.

However, Babcock said the ITF had the power to suspend Williams indefinitely form tournaments, including grand slams, and impose a heavy fine. It is believed that the ITF will settle for a fine in the region of $100,000.

Serena Williams won $560,000 at the US Open: her share of the doubles was $210,000 and she earned $350,000 for reaching the semi-final. Her prize money this year is $4m.

Williams made a statement after the incident but she was criticised for not showing enough remorse. Before the doubles final yesterday, she issued another statement saying: “I want to amend my press statement of yesterday, and want to make it clear as possible.

“I want to sincerely apologise first to the lineswoman, Kim Clijsters, the USTA and mostly tennis fans everywhere for my inappropriate outburst.

“I’m a woman of great pride, faith and integrity, and I admit when I’m wrong. I need to make it clear to all young people that I handled myself inappropriately and it’s not the way to act – win or lose, good call or bad call in any sport, in any manner. I like to lead by example.

“We all learn from experiences both good and bad. I will learn and grow from this, and be a better person as a result.” At the trophy presentation, Serena said: “I want to thank the fans for supporting me through this.”

Patrick McEnroe, conducting an on-court interview, was booed as he pursued the matter. There was applause when Venus said: “I think the crowd is saying, ‘Let’s move on.”

But the ITF investigation ensures that the matter is not yet resolved.