The tennis obituaries will have to wait for now. The Williams sisters have no intentions of quitting anytime soon.

If they have their way, they will be around for a lot longer yet, perhaps adding records for longevity to their records on the court.

For years, people have speculated about how long they would stay in the game, predicting they would eventually lose motivation as they racked up the titles.

But the speculators have been wrong and Venus said the American sisters were more motivated than ever to keep going after a long injury layoff.

"We've decided we're not going to lead a traditional career," Venus said on Monday, with no hint of irony.

"We haven't to this point, so we won't. So we're going to play past the limit that anyone has ever played."

Venus is 31 and has not won a Grand Slam singles title since 2008. Apart from Wimbledon --which she has won five times -- she has not won any other major in a decade.

Serena turns 30 in four weeks. She won the last of her 14 Grand Slam titles last year, before she was struck down with health issues.

Serena told reporters on Monday that if Venus retired right now, she would keep playing because she loved the game so much but Venus said they were more likely to go at the same time.

"We have to go out together," Venus said. "When our singles game goes, we'll continue to dominate in doubles, hopefully bring home more majors in that.

"We've decided to just enjoy tennis. It's such an honour. We'll do it as long as we can. Right now the end is not really in sight."

Venus won her first round match at the US Open on Monday, beating Vesna Dolonts of Russia 6-4, 6-3. Serena opens her campaign on Tuesday, against Bojana Jovanovski of Serbia.